Name: modification and functionalization of the guanidine group by tailor-made precursors
Uploaded: 2017-04-27T13:00:00
Description: Watch this Scientific Journal Video about Modification and Functionalization of the Guanidine Group by Tailor-made Precursors at JoVE.com

T.G.K. acknowledges the International Graduate School for Science and Engineering (IGGSE) of the Technische Universit&#228;t M&#252;nchen for their financial support. H.K. acknowledges the Center for Integrated Protein Science Munich (CIPSM) for their support.

Note: All reagents and solvents were obtained from commercial suppliers and were used without further purification.
Caution: Please consult all relevant material safety data sheets (MSDS) before use. Please use all appropriate safety equipment when performing chemical syntheses (e.g., fume hood, safety glasses, gloves, lab coat, full-length pants, and closed-toe shoes).
1. Synthesis of the Guanidinylation Precursors
<ol>
	<li>Alkylated species
	<...

<ol>
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H., Davidson, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mercury+(II)+Comlexes+of+Guanidine+and+Ammonia,+and+a+general+discussion+of+the+Complexing+of+Mercury+(II)+by+Nitrogen+Bases.">Mercury (II) Comlexes of Guanidine and Ammonia, and a general discussion of the Complexing of Mercury (II) by Nitrogen Bases.</a> J. Am. Chem. Soc. 86 (20), 4325-4329 (1964).</li><li>Berlinck, R. G., Burtoloso, A. C., Kossuga, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+chemistry+and+biology+of+organic+guanidine+derivatives.">The chemistry and biology of organic guanidine derivatives.</a> Nat. Prod. Rep. 25, 919-954 (2008).</li><li>Peterlin-Ma&#353;i&#269;, L., Kikelj, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arginine+mimetics.">Arginine mimetics.</a> Tetrahedron. 57 (33), 7073-7105 (2001).</li><li>Peterlin-Ma&#353;i&#269;, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arginine+mimetic+structures+in+biologically+active+antagonists+and+inhibitors.">Arginine mimetic structures in biologically active antagonists and inhibitors.</a> Curr. Med. Chem. 13 (30), 3627-3648 (2006).</li><li>Hynes, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrins:+bidirectional,+allosteric+signaling+machines.">Integrins: bidirectional, allosteric signaling machines.</a> Cell. 110 (6), 673-687 (2002).</li><li>Liddington, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+aspects+of+integrins.">Structural aspects of integrins.</a> Adv. Exp. Med. Biol. 819, 111-126 (2014).</li><li>Plow, E. F., Haas, T. A., Zhang, L., Loftusi, J., Smith, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ligand+binding+to+integrins.">Ligand binding to integrins.</a> J. Biol. Chem. 275 (29), 21785-21788 (2000).</li><li>Kapp, T. G., Fottner, M., Maltsev, O. V., Kessler, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small+cause,+great+impact+-+modification+of+guanidine+group+in+RGD+controls+subtype+selectivity.">Small cause, great impact - modification of guanidine group in RGD controls subtype selectivity.</a> Angew. Chem. Int. Ed. 55, 1540-1543 (2016).</li><li>Xiong, J. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+the+extracellular+segment+of+integrin+alpha+Vbeta3.">Crystal structure of the extracellular segment of integrin alpha Vbeta3.</a> Science. 294, 339-345 (2001).</li><li>Xiong, J. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+the+extracellular+segment+of+integrin+alpha+Vbeta3+in+complex+with+an+Arg-Gly-Asp+ligand.">Crystal structure of the extracellular segment of integrin alpha Vbeta3 in complex with an Arg-Gly-Asp ligand.</a> Science. 296 (5565), 151-155 (2002).</li><li>Nagae, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+&#945;5&#946;1+integrin+ectodomain:+atomic+details+of+the+fibronectin+receptor.">Crystal structure of &#945;5&#946;1 integrin ectodomain: atomic details of the fibronectin receptor.</a> J. Cell Biol. 197 (1), 131-140 (2012).</li><li>Hersel, U., Dahmen, C., Kessler, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RGD+modified+polymers:+biomaterials+for+stimulated+cell+adhesion+and+beyond.">RGD modified polymers: biomaterials for stimulated cell adhesion and beyond.</a> Biomaterials. 24 (24), 4385-4415 (2003).</li><li>Auernheimer, J., Dahmen, C., Hersel, U., Bausch, A., Kessler, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoswitched+Cell+Adhesion+on+Surfaces+with+RGD+Peptides.">Photoswitched Cell Adhesion on Surfaces with RGD Peptides.</a> J. Am. Chem. 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Ed. 49 (48), 9278-9281 (2010).</li><li>Rossiter, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+substrate-based+inhibitors+of+mammalian+dimethylarginine+dimethylaminohydrolase.">Selective substrate-based inhibitors of mammalian dimethylarginine dimethylaminohydrolase.</a> J. Med. Chem. 48 (14), 4670-4678 (2005).</li><li>Weiss, S., Keller, M., Bernhardt, G., Buschauer, A., K&#246;nig, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N(G)-Acyl-argininamides+as+NPY+Y(1)+receptor+antagonists:+Influence+of+structurally+diverse+acyl+substituents+on+stability+and+affinity.">N(G)-Acyl-argininamides as NPY Y(1) receptor antagonists: Influence of structurally diverse acyl substituents on stability and affinity.</a> Bioorg. Med. 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The precursor for guanidinylation is an orthogonally deprotected cyclic peptide derivative, (c(OrnD(OtBu)Gf(NMe)V)), which is synthesized by a standard Fmoc protocol of solid-phase peptide synthesis (SPPS). Ornithin was used as the orthogonally protected derivative, (Fmoc-Orn(Dde)-OH), which can be deprotected with hydrazine in DMF after the cyclization of the peptide scaffold. The peptide precursor is purified by the precipitation of the compound and by the subsequent lyophilization.
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Among the most abundant pharmacophoric groups in natural ligands is the guanidine group, which is involved in multiple interactions1,2. For example, it serves as a potential four-fold hydrogen donor in hydrogen bond interactions and is involved in electrostatic interactions, such as salt bridges or cation-&#960; interactions. In medicinal chemistry, this group is often found in drugs and drug candidates4, although very often as guanidine mimetics5,6. The reason for the development of guanidine mimetics is the removal of the ubiquitous, positively charged guanidine group, as well as the adjustment of the lipophilicity of the ligand. In peptidic ligands, the only guanidine group-containing amino acid is arginine, which is therefore often found in the bioactive region of peptidic ligands.
A very prominent example for an arginine-containing ligand family is the subfamily of the RGD-binding integrins. In general, integrins are a class of cell adhesion receptors, which take over important functions in all higher organisms. Some of these functions involve cell adhesion, migration, and cell survival. Thus, they are also involved in pathological indications, such as cancer and fibrosis. Integrins are transmembrane heterodimeric proteins consisting of an &#945;- and a &#946;-subunit that form 24 currently known integrin subtypes; 8 of them recognize the tripeptide sequence Arg-Gly-Asp (=RGD) in their ligands7. The binding region is located at the interface between these two subtypes in the extracellular part, the so-called integrin head group8. RGD is recognized by two common interactions: the metal-ion-dependent adhesion site (MIDAS) region, which is located in the beta subunit and which binds the carboxylic acid in the ligands (side chain of Asp); and the guanidine group in the ligands, which is located in the alpha subunit. Most of the integrin subtypes are promiscuous and share at least a part of their natural extracellular matrix (ECM) ligands9. Thus, for the development of artificial integrin ligands, the major focus is, besides a high binding affinity, the subtype selectivity. Recently, we were able to unveil a key element for the generation of subtype-selective ligands: the guanidine group. Through distinct modifications, biselective ligands for the &#945;v- and &#945;5-containing integrin subtypes can be turned into selective compounds by simple modifications on the guanidine group, which can then discriminate the different &#945;-subunits10.
In the pocket of &#945;v, the guanidine group interacts side-on via a bidentate salt bridge with Asp21811,12. This interaction can also be observed in &#945;5&#946;1 (here, with Asp227 in &#945;5), but additionally, an end-on interaction of the guanidine group with a Gln residue (Gln221) is observed there13. Thus, we modified the guanidine group in two opposite ways: in one case, by blocking the side-on interaction with the methylation of the N&#948; of the guanidine group, and in the other case, with the methylation of the guanidine N&#969;, blocking the end-on interaction. Surprisingly, this small modification led to a complete selectivity shift in the ligands. In addition to the alkylation, a new functionalization method was introduced in this publication. The classical functionalization method for this type of pentapeptidic ligand is through the side-chain conjugation of an amino acid not involved in binding (e.g., K in c(RGDfK))14,15. Here, we show that functionalization is also possible by modifying the guanidine &#8212; which is crucial for binding &#8212; with an acyl or alkylated linker. The positive charge that is essential for binding is retained, and models suggest that the long chain points out of the binding pocket, thus providing an ideal possibility for the attachment of further linkers and labeling units (e.g., a fluorescent label or a chelator for molecular imaging).
In this work, we concentrate on the preparative steps for the modification of the guanidine group in arginine-containing ligands. This involves the synthesis of N&#969;-methylated species, as well as guanidines with longer linker units. The different modifications comprise acyl and alkyl groups.

<table border="0" cellpadding="0" cellspacing="0" width="758">
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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">N,N&#8242;-Di-Boc-1H-pyrazole-1-carboxamidine, 98%&#160;</td>
			<td style="width:151px;">Sigma Aldrich</td>
			<td style="width:176px;">434167&#160;ALDRICH</td>
			<td style="width:111px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:323px;">Triphenylphosphine, 99%</td>
			<td>Sigma Aldrich</td>
			<td>T84409&#160;SIGMA-ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tetrahydrofuran, &#62;99.5%</td>
			<td>Carl Roth</td>
			<td>4745</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tetrahydrofuran anhydrous, 99.8%</td>
			<td>Carl Roth</td>
			<td>5182</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Methanol anhydrous, 99.8%</td>
			<td>Sigma Aldrich</td>
			<td>322415&#160;SIGMA-ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diisopropyl azodicarboxylate, 98%</td>
			<td>Sigma Aldrich</td>
			<td>225541&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dichlormethan, for synthesis, 99.5%</td>
			<td>Carl Roth</td>
			<td>8424</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Silica gel for flash chromtaography</td>
			<td>Sigma Aldrich</td>
			<td>60738&#160;SIGMA-ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">n-Pentane, 99%</td>
			<td>Carl Roth</td>
			<td>8720</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">n-Hexane, 99%</td>
			<td>Carl Roth</td>
			<td>CP47</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethylacetate, 99.5%</td>
			<td>Carl Roth</td>
			<td>7338</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Aminohexanol, 95%</td>
			<td>Sigma Aldrich</td>
			<td>A56353&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">S-Methylisothiourea hemisulfate, 98%</td>
			<td>Sigma Aldrich</td>
			<td>M84445 ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Di-tert-butyl dicarbonate, 99%</td>
			<td>Sigma Aldrich</td>
			<td>205249&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">N,N-Dimethylformamid, 99.8%</td>
			<td>Carl Roth</td>
			<td>A529</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">N,N-Diisopropylethylamin, 99.5%</td>
			<td>Carl Roth</td>
			<td>2474</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Acetic anhydrid, 99%</td>
			<td>Carl Roth</td>
			<td>4483</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Chlortrityl resin</td>
			<td>Carbolution</td>
			<td>CC11006</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fmoc-Gly-OH, 98%</td>
			<td>Carbolution</td>
			<td>CC05014</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Piperidin, 99%</td>
			<td>Sigma Aldrich</td>
			<td>104094&#160;SIGMA-ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fmoc-Orn(Dde)-OH</td>
			<td>Iris-Biotech</td>
			<td>FAA1502</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HATU, 99%</td>
			<td>Carbolution</td>
			<td>CC01011</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HOAt, 99%</td>
			<td>Carbolution</td>
			<td>CC01004</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fmoc-Val-OH</td>
			<td>Carbolution</td>
			<td>CC05028</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2-Nitrobenzenesulfonyl chloride, 97%</td>
			<td>Sigma Aldrich</td>
			<td>N11507&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2,4,6-Collidine, 99%</td>
			<td>Sigma Aldrich</td>
			<td>27690&#160;SIGMA-ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mercaptoethanol, 99%&#160;</td>
			<td>Sigma Aldrich</td>
			<td>M6250&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diazabicycloundecen, 98%</td>
			<td>Sigma Aldrich</td>
			<td>139009&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fmoc-D-Phe-OH, 98%</td>
			<td>Sigma Aldrich</td>
			<td>47378&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fmoc-Asp(OtBu)-OH, 98%</td>
			<td>Carbolution</td>
			<td>CC05008</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hexafluoroisopropanol</td>
			<td>Carbolution</td>
			<td>CC03056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diphenylphosphoryl azide, 97%</td>
			<td>Sigma Aldrich</td>
			<td>178756&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TFA, 99.9%</td>
			<td>Carl Roth</td>
			<td>P088</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Triisopropylsilan, 98%</td>
			<td>Sigma Aldrich</td>
			<td>233781&#160;ALDRICH</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Acetonitrile, HPLC grade</td>
			<td>Carl Roth</td>
			<td>HN44</td>
			<td></td>
		</tr>
	</tbody>
</table>

modification and functionalization of the guanidine group by tailor-made precursors

The guanidine group is one of the most important pharmacophoric groups in medicinal chemistry. The only amino acid carrying a guanidine group is arginine. In this article, an easy method for the modification of the guanidine group in peptidic ligands is provided, with an example of RGD-binding integrin ligands. It was recently demonstrated that the distinct modification of the guanidine group in these ligands allows for the selective modulation of the subtype (e.g., between the subtypes &#945;v and &#945;5). Moreover, a formerly unknown strategy for the functionalization via the guanidine group was demonstrated, and the synthetic approach is reviewed in this document. The modifications described here involve terminally (N&#969;) alkylated and acetylated guanidine groups. For the synthesis, tailor-made precursor molecules are synthesized, which are then subjected to a reaction with an orthogonally deprotected amine to transfer the pre-modified guanidine group. For the synthesis of alkylated guanidines, precursors based on N,N&#8242;-Di-Boc-1H-pyrazole-1-carboxamidine are used to synthesize acylated compounds, the precursor of choice being a correspondingly acylated derivative of N-Boc-S-methylisothiourea, which can be obtained in one- and two-step reactions.

The cyclic peptide precursor was synthesized as a linear peptide, cyclized, and orthogonally Dde-deprotected. After the precipitation, the purity of the compound was analyzed with HPLC-MS (Figure 1). To monitor the progress of the reaction, an HPLC analysis was performed after the 2-h reaction time (Figure 2).
For larger residues on the guanidine group, the reaction time of 2 h is often not enou...

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Modification and Functionalization of the Guanidine Group by Tailor-made Precursors

A protocol for the synthesis of alkyl-modified guanidines based on the use of the corresponding precursors is presented.

The guanidine group is one of the most important pharmacophoric groups in medicinal chemistry. The only amino acid carrying a guanidine group is arginine. ...

The overall goal of this procedure is to provide a convenient synthetic access to guanidine functionalized peptides. This method can help answer key questions in the field of muscle peptide chemistry such as the development of integrin ligands or GPCR ligands. The main advantage of this technique is that it allows an easy, synthetic access to functionalized guanidines, completely compatible with SPPS.The technology will be especially valuable for tactile molecules because the functional groups, which are modified, are typically deteriorating biomolecules. In our case, we aim for molecules which can be used fpr molecular imaging of distinct properties of individual cancers and for their specific treatment;an important issue for personalized medicine. To begin this specific procedure, add one gram of boc-pyrazol carboxamaidine and one gram of PPh3 to a 50 milliliter round-bottomed flask.Subsequently, add 10 milliliters of dried THF to a 50 milliliter round-bottomed flask in an inert atmosphere via a rubber septum. Using a syringe, add 194 microliters of dry methanol. Stir the solution at room temperature.Using a syringe, add a prepared solution of diisopropyl azodicarboxylate in THF dropwise over 15 minutes. Then, let the solution stir for two hours at room temperature. Using a rotary evaporator, remove the solvent under reduced pressure.After this, dissolve the crude product in one milliliter of DCM. Next, let a let a flash column with 100 grams of silica, in 10%ethyl acetate in a pentane solution. Load the dissolved crude product on the column and add the the solvent under pressure.Collect, identify and combine the fractions as outlined in the text protocol. Then, using a rotary evaporator, evaporate the solvent under reduced pressure to obtain the desired compound as a yellow, viscous oil. First, add one gram of boc-pyrazole carboxamidine, one gram of PPH3 and 0.9 grams of Dde-6-Aminohexanol to a 50 milliliter round-bottomed flask.Then, add 10 milliliters of dry THF in an inert atmosphere using a rubber septum. Afterwards, dissolve the starting materials at room temperature. Using a syringe, add a prepared solution of diisopropyl azodicarboxylate in THF dropwise over 15 minutes.Stir the solution for two hours at room temperature. After this, use a rotary evaporator to remove the solvent under reduced pressure. Dissolve the crude product in 1 milliliter of DCM.Next, load a flash column with 100 grams of silica in a two to one solution of pentane and ethyl acetate. Load the dissolved crude product on the column and add the solvent under pressure. Collect, identify and combine the fractions as outlined in the text protocol.Using a rotary evaporator, evaporate the solvent under reduced pressure to obtain the desired product. To begin, dissolve 1.4 grams of S-methylisothiourea and 2.2 grams of boc-anhydride in a vigorously-stirring biphasic solution of DCM and saturated aqueous sodium bicarbonate. Let the mixture stir for 24 hours at room temperature.After this, pour the mixture into a separatory funnel. Separate the layers and extract the aqueous phase three times with DCM. Then, combine the organic phases.Dry the combined organic phases with sodium sulfate. After removing the solvent using a rotary evaporator, dissolve the crude product in 2 milliliters of hexane. Load a flash column with 100 grams of silica in a four to one solution of hexane and ethyl acetate.After this, load the dissolved crude product on the column and add the solvent under pressure. After collecting and identifying the fractions, combine the desired fractions. Using a rotary evaporator, evaporate the solvent under reduced pressure to obtain 1.1 grams of Boc-S-methylisothiourea.Dissolve 250 milligrams of the collected Boc-S-methylisothiourea in 10 milliliters of dried DMF in a 50 milliliter round-bottomed flask in an inert atmosphere at room temperature. Use a syringe to add 440 microliters of DIPEA. Using a syringe, add 245 microliters of acetic anhydride dropwise while stirring.Let the mixture stir for one hour at room temperature. Then, use a syringe to add two milliliters of methanol and stir for 15 minutes. After removing the solvent under reduced pressure, using a rotary evaporator, dissolve the crude product in one milliliter of DCM.Load a flash column with 60 grams of silica in a three to one solution of hexane and ethyl acetate. Next, load the dissolved crude product and add the solvent under pressure. Collect, identify and combine the fractions as outlined in the text protocol.Using a rotary evaporator, evaporate the solvent under reduced pressure to obtain 210 milligrams of the desired product as a white solid. To begin, dissolve a small amount of the orthogonally deprotected cyclic peptide in a small volume of DMF. Add two equivalents of DIPEA.And two equivalents of the guanidinylation precursor. Then, let the solution stir for two hours at room temperature. Once the reaction is complete, remove the solvent.Re-dissolve the guanidinylated cyclic peptide in acetyl nitrile and perform semi-preparative HPLC purification as outlined in the text protocol. After this, in a small glass vile, add a prepared solution of trifluoroacetic acid, water and triisopropylsilane to the purified product. Stir this mixture for one hour at room temperature, and then observe the complete deprotection with ESIMS.Add 10 milliliters of ice-cold ether to a 50 milliliters centrifuge tube. Using a Pasteur pipette, add the deprotected peptide dropwise to the ether. Centrifuge the suspension at 5, 000 times g for five minutes.After this, wash the pellet with ice-cold ether. In centrifuge at 5, 000 times g for five minutes. Repeat this washing and centrifugation once more.Then, dissolve the product in 2 milliliters of HBLC-grade water and purify the product using semi-preparative HPLC as outlined in the text protocol. In this study, an easy method in the modification of the guanidine group in peptidic glygins is presented. The reactions'progress is monitored using high-pressure liquid chromatography.For larger residues on the guanidine group, two hours is often not enough time for the reaction to reach completion. Thus, the reaction is continued and the compounds are purified by semi-preparative HPLC. A small amount is then diluted with DMSO to obtain a stem solution for the biological evaluation in an al-ee-so-like solid phase binding assay.All the compounds analyzed show a relatively high affinity of the integrant subtype alpha v beta three, And high selectivity against the integrant subtype alpha five beta one. We first had the idea for this method when we were looking for a standard method for guanidinylation during SPPS. After watching this video, you should have a good understanding of how to prepare tailor made guanidinylation precursors, in order to modify or functionalize the guanidine group of your target peptide.

modification-functionalization-guanidine-group-tailor-made

Research

JoVE Journal

Biochemistry

Thermostabilization, Expression, Purification, and Crystallization of the Human Serotonin Transporter Bound to S-citalopram

The serotonin transporter is a sodium and chloride-coupled transporter that &#34;pumps&#34; extracellular serotonin into cells. S-citalopram is a drug used to treat depression and anxiety by binding to the serotonin transporter with high-affinity, blocking serotonin reuptake. Here we report an efficient procedure and a set of tools to stabilize, express, purify, and crystallize serotonin transporter-antibody complexes bound to S-citalopram and other antidepressants. Mutations which stabilize the serotonin transporter were identified using an S-citalopram binding assay. Serotonin transporter expressed in baculovirus-transduced HEK293S GnTI- cells, was reconstituted into proteoliposomes and used to raise high-affinity antibodies. We have developed a strategy to discover antibodies that are useful for structural studies. A straightforward approach for the expression of antibody fragments in Sf9 cells has also been established. Transporter-antibody complexes purified using this procedure are well-behaved and readily crystallize, producing complexes with S-citalopram that diffract X-rays to 3-4 &#197; resolution. The strategies developed here can be utilized to determine the structure of other challenging membrane proteins.

Thermostabilization, Expression, Purification, and Crystallization of the Human Serotonin Transporter Bound to S-citalopram

This manuscript describes how to screen for thermostabilizing mutations, purify the human serotonin transporter, generate high affinity antibodies, and crystallize the serotonin transporter-antibody complex bound to the antidepressant drug S-citalopram. This protocol can be adapted to the study of other challenging membrane transporters, receptors, and channels.

The serotonin transporter is a sodium and chloride-coupled transporter that &#34;pumps&#34; extracellular serotonin into cells. S-citalopram is a drug ...

Rab10 Phosphorylation Detection by LRRK2 Activity Using SDS-PAGE with a Phosphate-binding Tag

Mutations in leucine-rich repeat kinase 2 (LRRK2) have been shown to be linked with familial Parkinson&#39;s disease (FPD). Since abnormal activation of the kinase activity of LRRK2 has been implicated in the pathogenesis of PD, it is essential to establish a method to evaluate the physiological levels of the kinase activity of LRRK2. Recent studies revealed that LRRK2 phosphorylates members of the Rab GTPase family, including Rab10, under physiological conditions. Although the phosphorylation of endogenous Rab10 by LRRK2 in cultured cells could be detected by mass spectrometry, it has been difficult to detect it by immunoblotting due to the poor sensitivity of currently available phosphorylation-specific antibodies for Rab10. Here, we describe a simple method of detecting the endogenous levels of Rab10 phosphorylation by LRRK2 based on immunoblotting utilizing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) combined with a phosphate-binding tag (P-tag), which is N-(5-(2-aminoethylcarbamoyl)pyridin-2-ylmetyl)-N,N&#39;,N&#39;-tris(pyridin-2-yl-methyl)-1,3-diaminopropan-2-ol. The present protocol not only provides an example of the methodology utilizing the P-tag but also enables the assessment of how mutations as well as inhibitor treatment/administration or any other factors alter the downstream signaling of LRRK2 in cells and tissues.

The present study describes a simple method of detecting endogenous levels of Rab10 phosphorylation by leucine-rich repeat kinase 2.

Mutations in leucine-rich repeat kinase 2 (LRRK2) have been shown to be linked with familial Parkinson&#39;s disease (FPD). Since abnormal activation of ...

Imaging of Extracellular Vesicles by Atomic Force Microscopy

Exosomes and other extracellular vesicles (EVs) are molecular complexes consisting of a lipid membrane vesicle, its surface decoration by membrane proteins and other molecules, and diverse luminal content inherited from a parent cell, which includes RNAs, proteins, and DNAs. The characterization of the hydrodynamic sizes of EVs, which depends on the size of the vesicle and its coronal layer formed by surface decorations, has become routine. For exosomes, the smallest of EVs, the relative difference between the hydrodynamic and vesicles sizes is significant. The characterization of vesicles sizes by the cryogenic transmission electron microscopy (cryo-TEM) imaging, a gold standard technique, remains a challenge due to the cost of the instrument, the expertise required to perform the sample preparation, imaging and data analysis, and a small number of particles often observed in images. A widely available and accessible alternative is the atomic force microscopy (AFM), which can produce versatile data on three-dimensional geometry, size, and other biophysical properties of extracellular vesicles. The developed protocol guides the users in utilizing this analytical tool and outlines the workflow for the analysis of EVs by the AFM, which includes the sample preparation for imaging EVs in hydrated or desiccated form, the electrostatic immobilization of vesicles on a substrate, data acquisition, its analysis, and interpretation. The representative results demonstrate that the fixation of EVs on the modified mica surface is predictable, customizable, and allows the user to obtain sizing results for a large number of vesicles. The vesicle sizing based on the AFM data was found to be consistent with the cryo-TEM imaging.&#160;

A step-by-step procedure is described for label-free immobilization of exosomes and extracellular vesicles from liquid samples and their imaging by atomic force microscopy (AFM). The AFM images are used to estimate the size of the vesicles in the solution and characterize other biophysical properties.&#160;

Exosomes and other extracellular vesicles (EVs) are molecular complexes consisting of a lipid membrane vesicle, its surface decoration by membrane ...

Mitochondria and Endoplasmic Reticulum Imaging by Correlative Light and Volume Electron Microscopy

Cellular organelles, such as mitochondria and endoplasmic reticulum (ER), create a network to perform a variety of functions. These highly curved structures are folded into various shapes to form a dynamic network depending on the cellular conditions. Visualization of this network between mitochondria and ER has been attempted using super-resolution fluorescence imaging and light microscopy; however, the limited resolution is insufficient to observe the membranes between the mitochondria and ER in detail. Transmission electron microscopy provides good membrane contrast and nanometer-scale resolution for the observation of cellular organelles; however, it is exceptionally time-consuming when assessing the three-dimensional (3D) structure of highly curved organelles. Therefore, we observed the morphology of mitochondria and ER via correlative light-electron microscopy (CLEM) and volume electron microscopy techniques using enhanced ascorbate peroxidase 2 and horseradish peroxidase staining. An en bloc staining method, ultrathin serial sectioning (array tomography), and volume electron microscopy were applied to observe the 3D structure. In this protocol, we suggest a combination of CLEM and 3D electron microscopy to perform detailed structural studies of mitochondria and ER.

We present a protocol to study the distribution of mitochondria and endoplasmic reticulum in whole cells after genetic modification using correlative light and volume electron microscopy including ascorbate peroxidase 2 and horseradish peroxidase staining, serial sectioning of cells with and without the target gene in the same section, and serial imaging via electron microscopy.

Cellular organelles, such as mitochondria and endoplasmic reticulum (ER), create a network to perform a variety of functions. These highly curved ...

Real-Time, Semi-Automated Fluorescent Measurement of the Airway Surface Liquid pH of Primary Human Airway Epithelial Cells

In recent years, the importance of mucosal surface pH in the airways has been highlighted by its ability to regulate airway surface liquid (ASL) hydration, mucus viscosity and activity of antimicrobial peptides, key parameters involved in innate defense of the lungs. This is of primary relevance in the field of chronic respiratory diseases such as cystic fibrosis (CF) where these parameters are dysregulated. While different groups have studied ASL pH both in vivo and in vitro, their methods report a relatively wide range of ASL pH values and even contradictory findings regarding any pH differences between non-CF and CF cells. Furthermore, their protocols do not always provide enough details in order to ensure reproducibility, most are low throughput and require expensive equipment or specialized knowledge to implement, making them difficult to establish in most labs. Here we describe a semi-automated fluorescent plate reader assay that enables the real-time measurement of ASL pH under thin film conditions that more closely resemble the in vivo situation. This technique allows for stable measurements for many hours from multiple airway cultures simultaneously and, importantly, dynamic changes in ASL pH in response to agonists and inhibitors can be monitored. To achieve this, the ASL of fully differentiated primary human airway epithelial cells (hAECs) are stained overnight with a pH-sensitive dye in order to allow for the reabsorption of the excess fluid to ensure thin film conditions. After fluorescence is monitored in the presence or absence of agonists, pH calibration is performed in situ to correct for volume and dye concentration. The method described provides the required controls to make stable and reproducible ASL pH measurements, which ultimately could be used as a drug discovery platform for personalized medicine, as well as adapted to other epithelial tissues and experimental conditions, such as inflammatory and/or host-pathogen models.

We present a protocol to make dynamic measurements of the airway surface liquid pH under thin film conditions using a plate-reader.

In recent years, the importance of mucosal surface pH in the airways has been highlighted by its ability to regulate airway surface liquid (ASL) ...

High-Throughput Total Internal Reflection Fluorescence and Direct Stochastic Optical Reconstruction Microscopy Using a Photonic Chip

Total internal reflection fluorescence (TIRF) is commonly used in single molecule localization based super-resolution microscopy as it gives enhanced contrast due to optical sectioning. The conventional approach is to use high numerical aperture microscope TIRF objectives for both excitation and collection, severely limiting the field of view and throughput. We present a novel approach to generating TIRF excitation for imaging with optical waveguides, called chip-based nanoscopy. The aim of this protocol is to demonstrate how chip-based imaging is performed in an already built setup. The main advantage of chip-based nanoscopy is that the excitation and collection pathways are decoupled. Imaging can then be done with a low magnification lens, resulting in large field of view TIRF images, at the price of a small reduction in resolution. Liver sinusoidal endothelial cells (LSECs) were imaged using direct stochastic optical reconstruction microscopy (dSTORM), showing a resolution comparable to traditional super-resolution microscopes. In addition, we demonstrate the high-throughput capabilities by imaging a 500 &#181;m x 500 &#181;m region with a low magnification lens, providing a resolution of 76 nm. Through its compact character, chip-based imaging can be retrofitted into most common microscopes and can be combined with other on-chip optical techniques, such as on-chip sensing, spectroscopy, optical trapping, etc. The technique is thus ideally suited for high throughput 2D super-resolution imaging, but also offers great opportunities for multi-modal analysis.

Chip-based super-resolution optical microscopy is a novel approach to fluorescence microscopy and offers advantages in cost effectiveness and throughput. Here, the protocols for chip preparation and imaging are shown for TIRF microscopy and localization-based super-resolution microscopy.

Total internal reflection fluorescence (TIRF) is commonly used in single molecule localization based super-resolution microscopy as it gives enhanced ...

Obtaining High-Quality Transcriptome Data from Cereal Seeds by a Modified Method for Gene Expression Profiling

The characterization of gene expression is dependent on RNA quality. In germinating, developing and mature cereal seeds, the extraction of high-quality RNA is often hindered by high starch and sugar content. These compounds can reduce both the yield and the quality of the extracted total RNA. The deterioration in quantity and quality of total RNA can subsequently have a significant impact on the downstream transcriptomic analyses, which may not accurately reflect the spatial and/or temporal variation in the gene expression profile of the samples being tested. In this protocol, we describe an optimized method for extraction of total RNA with sufficient quantity and quality to be used for whole transcriptome analysis of cereal grains. The described method is suitable for several downstream applications used for transcriptomic profiling of developing, germinating, and mature cereal seeds. The method of transcriptome profiling using a microarray platform is shown. This method is specifically designed for gene expression profiling of cereals with described genome sequences. The detailed procedure from microarray handling to final quality control is described. This includes cDNA synthesis, cRNA labelling, microarray hybridization, slide scanning, feature extraction, and data quality validation. The data generated by this method can be used to characterize the transcriptome of cereals during germination, in various stages of grain development, or at different biotic or abiotic stress conditions. The results presented here exemplify high-quality transcriptome data amenable for downstream bioinformatics analyses, such as the determination of differentially expressed genes (DEGs), characterisation of gene regulatory networks, and conducting transcriptome-wide association study (TWAS).

A method for transcriptome profiling of cereals is presented. The microarray-based gene expression profiling starts with the isolation of high-quality total RNA from cereal grains and continues with the generation of cDNA. After cRNA labelling and microarray hybridization, recommendations are given for signal detection and quality control.

The characterization of gene expression is dependent on RNA quality. In germinating, developing and mature cereal seeds, the extraction of high-quality ...

Analysis of SEC-SAXS data via EFA deconvolution and Scatter

BioSAXS is a popular technique used in molecular and structural biology to determine the solution structure, particle size and shape, surface-to-volume ratio and conformational changes of macromolecules and macromolecular complexes. A high quality SAXS dataset for structural modeling must be from monodisperse, homogeneous samples and this is often only reached by a combination of inline chromatography and immediate SAXS measurement. Most commonly, size-exclusion chromatography is used to separate samples and exclude contaminants and aggregations from the particle of interest allowing SAXS measurements to be made from a well-resolved chromatographic peak of a single protein species. Still, in some cases, even inline purification is not a guarantee of monodisperse samples, either because multiple components are too close to each other in size or changes in shape induced through binding alter perceived elution time. In these cases, it may be possible to deconvolute the SAXS data of a mixture to obtain the idealized SAXS curves of individual components. Here, we show how this is achieved and the practical analysis of SEC-SAXS data is performed on ideal and difficult samples. Specifically, we show the SEC-SAXS analysis of the vaccinia E9 DNA polymerase exonuclease minus mutant.

SEC-BioSAXS measurements of biological macromolecules are a standard approach for determining solution structure of macromolecules and their complexes. Here, we analyze SEC-BioSAXS data from two types of commonly encountered SEC traces&#8212;chromatograms with fully resolved and partially resolved peaks. We demonstrate the analysis and deconvolution using scatter and BioXTAS RAW.

BioSAXS is a popular technique used in molecular and structural biology to determine the solution structure, particle size and shape, surface-to-volume ...

Removal and Replacement of Endogenous Ligands from Lipid-Bound Proteins and Allergens

Many major allergens bind to hydrophobic lipid-like molecules, including Mus m 1, Bet v 1, Der p 2, and Fel d 1. These ligands are strongly retained and have the potential to influence the sensitization process either through directly stimulating the immune system or altering the biophysical properties of the allergenic protein. In order to control for these variables, techniques are required for the removal of endogenously bound ligands and, if necessary, replacement with lipids of known composition. The cockroach allergen Bla g 1 encloses a large hydrophobic cavity which binds a heterogeneous mixture of endogenous lipids when purified using traditional techniques. Here, we describe a method through which these lipids are removed using reverse-phase HPLC followed by thermal annealing to yield Bla g 1 in either its Apo-form or reloaded with a user-defined mixture of fatty acid or phospholipid cargoes. Coupling this protocol with biochemical assays reveal that fatty acid cargoes significantly alter the thermostability and proteolytic resistance of Bla g 1, with downstream implications for the rate of T-cell epitope generation and allergenicity. These results highlight the importance of lipid removal/reloading protocols such as the one described herein when studying allergens from both recombinant and natural sources. The protocol is generalizable to other allergen families including lipocalins (Mus m 1), PR-10 (Bet v 1), MD-2 (Der p 2) and Uteroglobin (Fel d 1), providing a valuable tool to study the role of lipids in the allergic response.

This protocol describes the removal of endogenous lipids from allergens, and their replacement with user-specified ligands through reverse-phase HPLC coupled with thermal annealing. 31P-NMR and circular dichroism allow for the rapid confirmation of ligand removal/loading, and the recovery of native allergen structure.

Many major allergens bind to hydrophobic lipid-like molecules, including Mus m 1, Bet v 1, Der p 2, and Fel d 1. These ligands are strongly retained and ...

Workflow and Tools for Crystallographic Fragment Screening at the Helmholtz-Zentrum Berlin

Fragment screening is a technique that helps to identify promising starting points for ligand design. Given that crystals of the target protein are available and display reproducibly high-resolution X-ray diffraction properties, crystallography is among the most preferred methods for fragment screening because of its sensitivity. Additionally, it is the only method providing detailed 3D information of the binding mode of the fragment, which is vital for subsequent rational compound evolution. The routine use of the method depends on the availability of suitable fragment libraries, dedicated means to handle large numbers of samples, state-of-the-art synchrotron beamlines for fast diffraction measurements and largely automated solutions for the analysis of the results.
Here, the complete practical workflow and the included tools on how to conduct crystallographic fragment screening (CFS) at the Helmholtz-Zentrum Berlin (HZB) are presented. Preceding this workflow, crystal soaking conditions as well as data collection strategies are optimized for reproducible crystallographic experiments. Then, typically in a one to two-day procedure, a 96-membered CFS-focused library provided as dried ready-to-use plates is employed to soak 192 crystals, which are then flash-cooled individually. The final diffraction experiments can be performed within one day at the robot-mounting supported beamlines BL14.1 and BL14.2 at the BESSY&#160; II electron storage ring operated by the HZB in Berlin-Adlershof (Germany). Processing of the crystallographic data, refinement of the protein structures, and hit identification is fast and largely automated using specialized software pipelines on dedicated servers, requiring little user input.
Using the CFS workflow at the HZB enables routine screening experiments. It increases the chances for successful identification of fragment hits as starting points to develop more potent binders, useful for pharmacological or biochemical applications.

Crystallographic fragment screening at the Helmholtz-Zentrum Berlin is performed using a workflow with dedicated compound libraries, crystal handling tools, fast data collection facilities&#160;and largely automated data analysis. The presented protocol intends to maximize the output of such experiments to provide promising starting points for downstream structure-based ligand design.

Fragment screening is a technique that helps to identify promising starting points for ligand design. Given that crystals of the target protein are ...