Name: voltage-clamp fluorometry in xenopus oocytes using fluorescent unnatural amino acids
Uploaded: 2017-05-27T13:00:00
Description: Watch this Scientific Journal Video about Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids at JoVE.com

pAnap was a kind gift from Dr. Peter Schultz (Scripps Research Institute). This work was funded by the Canadian Institutes for Health Research Grants MOP-102689 and MOP-136894 (to R.B.) and Canadian Foundation for Innovation Grant 950-225005.

Frog manipulations were performed in accordance with the Canadian guidelines and have been approved by the ethics committee (CDEA, protocol #15-042) of University of Montr&#233;al.
1. mRNA Preparation for fUAA Incorporation
<ol>
	<li>Choose a site of interest in the protein where conformational changes are expected to occur. Select an amino acid in this region to be substituted for the fUAA. 
	NOTE: The choice of position is based on the structural rearrangements that are expected. If a...

<ol>
	<li>Mannuzzu, L. M., Moronne, M. M., Isacoff, E. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+physical+measure+of+conformational+rearrangement+underlying+potassium+channel+gating.">Direct physical measure of conformational rearrangement underlying potassium channel gating.</a> Science. 271 (5246), 213-216 (1996).</li><li>Kalstrup, T., Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+internal+pore+opening+in+K(V)+channels+probed+by+a+fluorescent+unnatural+amino+acid.">Dynamics of internal pore opening in K(V) channels probed by a fluorescent unnatural amino acid.</a> Proc Natl Acad Sci U S A. 110 (20), 8272-8277 (2013).</li><li>Xiao, H., Schultz, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=At+the+Interface+of+Chemical+and+Biological+Synthesis:+An+Expanded+Genetic+Code.">At the Interface of Chemical and Biological Synthesis: An Expanded Genetic Code.</a> Cold Spring Harb Perspect Biol. 8 (9), (2016).</li><li>Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+9.">Chapter 9.</a> Handbook of Ion Channels. , 113-133 (2015).</li><li>Chatterjee, A., Guo, J., Lee, H. S., Schultz, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+genetically+encoded+fluorescent+probe+in+mammalian+cells.">A genetically encoded fluorescent probe in mammalian cells.</a> J Am Chem Soc. 135 (34), 12540-12543 (2013).</li><li>DeBerg, H. A., Brzovic, P. S., Flynn, G. E., Zagotta, W. N., Stoll, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+Energetics+of+Allosteric+Regulation+of+HCN2+Ion+Channels+by+Cyclic+Nucleotides.">Structure and Energetics of Allosteric Regulation of HCN2 Ion Channels by Cyclic Nucleotides.</a> J Biol Chem. 291 (1), 371-381 (2016).</li><li>Shen, B., 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=Genetically+encoding+unnatural+amino+acids+in+neural+stem+cells+and+optically+reporting+voltage-sensitive+domain+changes+in+differentiated+neurons.">Genetically encoding unnatural amino acids in neural stem cells and optically reporting voltage-sensitive domain changes in differentiated neurons.</a> Stem Cells. 29 (8), 1231-1240 (2011).</li><li>Aman, T. K., Gordon, S. E., Zagotta, W. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+CNGA1+Channel+Gating+by+Interactions+with+the+Membrane.">Regulation of CNGA1 Channel Gating by Interactions with the Membrane.</a> J Biol Chem. 291 (19), 9939-9947 (2016).</li><li>Haddad, G. A., Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mode+shift+of+the+voltage+sensors+in+Shaker+K++channels+is+caused+by+energetic+coupling+to+the+pore+domain.">Mode shift of the voltage sensors in Shaker K+ channels is caused by energetic coupling to the pore domain.</a> J Gen Physiol. 137 (5), 455-472 (2011).</li><li>Batulan, Z., Haddad, G. A., Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+intersubunit+interaction+between+S4-S5+linker+and+S6+is+responsible+for+the+slow+off-gating+component+in+Shaker+K++channels.">An intersubunit interaction between S4-S5 linker and S6 is responsible for the slow off-gating component in Shaker K+ channels.</a> J Biol Chem. 285 (18), 14005-14019 (2010).</li><li>Kusch, J., 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=How+subunits+cooperate+in+cAMP-induced+activation+of+homotetrameric+HCN2+channels.">How subunits cooperate in cAMP-induced activation of homotetrameric HCN2 channels.</a> Nat Chem Biol. 8 (2), 162-169 (2012).</li><li>Lee, H. S., Guo, J., Lemke, E. A., Dimla, R. D., Schultz, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+incorporation+of+a+small,+environmentally+sensitive,+fluorescent+probe+into+proteins+in+Saccharomyces+cerevisiae.">Genetic incorporation of a small, environmentally sensitive, fluorescent probe into proteins in Saccharomyces cerevisiae.</a> J Am Chem Soc. 131 (36), 12921-12923 (2009).</li><li>Summerer, D., 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=A+genetically+encoded+fluorescent+amino+acid.">A genetically encoded fluorescent amino acid.</a> Proc Natl Acad Sci U S A. 103 (26), 9785-9789 (2006).</li><li>Kalstrup, T., Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reinitiation+at+non-canonical+start+codons+leads+to+leak+expression+when+incorporating+unnatural+amino+acids.">Reinitiation at non-canonical start codons leads to leak expression when incorporating unnatural amino acids.</a> Sci Rep. 5, 11866 (2015).</li><li>Liu, H., Naismith, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+efficient+one-step+site-directed+deletion,+insertion,+single+and+multiple-site+plasmid+mutagenesis+protocol.">An efficient one-step site-directed deletion, insertion, single and multiple-site plasmid mutagenesis protocol.</a> BMC Biotechnol. 8, 91 (2008).</li><li>Beckert, B., Masquida, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+RNA+by+in+vitro+transcription.">Synthesis of RNA by in vitro transcription.</a> Methods Mol Biol. 703, 29-41 (2011).</li><li>Goldin, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maintenance+of+Xenopus+laevis+and+oocyte+injection.">Maintenance of Xenopus laevis and oocyte injection.</a> Methods Enzymol. 207, 266-279 (1992).</li><li>Rudokas, M. W., Varga, Z., Schubert, A. R., Asaro, A. B., Silva, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Xenopus+oocyte+cut-open+vaseline+gap+voltage-clamp+technique+with+fluorometry.">The Xenopus oocyte cut-open vaseline gap voltage-clamp technique with fluorometry.</a> J Vis Exp. (85), (2014).</li><li>Zhao, J., Blunck, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+isolated+voltage+sensing+domain+of+the+Shaker+potassium+channel+forms+a+voltage-gated+cation+channel.">The isolated voltage sensing domain of the Shaker potassium channel forms a voltage-gated cation channel.</a> Elife. 5, (2016).</li><li>Posson, D. J., Ge, P., Miller, C., Bezanilla, F., Selvin, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small+vertical+movement+of+a+K++channel+voltage+sensor+measured+with+luminescence+energy+transfer.">Small vertical movement of a K+ channel voltage sensor measured with luminescence energy transfer.</a> Nature. 436 (7052), 848-851 (2005).</li><li>Chanda, B., Asamoah, O. K., Blunck, R., Roux, B., Bezanilla, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gating+charge+displacement+in+voltage-gated+ion+channels+involves+limited+transmembrane+movement.">Gating charge displacement in voltage-gated ion channels involves limited transmembrane movement.</a> Nature. 436 (7052), 852-856 (2005).</li><li>Taraska, J. W., Puljung, M. C., Zagotta, W. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Short-distance+probes+for+protein+backbone+structure+based+on+energy+transfer+between+bimane+and+transition+metal+ions.">Short-distance probes for protein backbone structure based on energy transfer between bimane and transition metal ions.</a> Proc Natl Acad Sci U S A. 106 (38), 16227-16232 (2009).</li><li>Baker, B. J., 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=Genetically+encoded+fluorescent+sensors+of+membrane+potential.">Genetically encoded fluorescent sensors of membrane potential.</a> Brain Cell Biol. 36 (1-4), 53-67 (2008).</li><li>Miranda, 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=State-dependent+FRET+reports+calcium-+and+voltage-dependent+gating-ring+motions+in+BK+channels.">State-dependent FRET reports calcium- and voltage-dependent gating-ring motions in BK channels.</a> Proc Natl Acad Sci U S A. , (2013).</li><li>Sisido, M., Ninomiya, K., Ohtsuki, T., Hohsaka, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Four-base+codon/anticodon+strategy+and+non-enzymatic+aminoacylation+for+protein+engineering+with+non-natural+amino+acids.">Four-base codon/anticodon strategy and non-enzymatic aminoacylation for protein engineering with non-natural amino acids.</a> Methods. 36 (3), 270-278 (2005).</li><li>Hohsaka, T., Ashizuka, Y., Murakami, H., Sisido, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Five-base+codons+for+incorporation+of+nonnatural+amino+acids+into+proteins.">Five-base codons for incorporation of nonnatural amino acids into proteins.</a> Nucleic Acids Res. 29 (17), 3646-3651 (2001).</li></ol>

The in vivo aminoacylation of tRNAs which are continuously being transcribed together with the tRNA-synthetase, makes it possible to obtain high expression levels for fluorescence measurements. For efficient fUAA incorporation, it is critical that pAnap is correctly injected into the nucleus. Due to the uncertainty of the exact location of the nucleus, 10-40% of the DNA injections are expected to fail, resulting in non-expressing (or leak-expressing) oocytes. Therefore, it is important to check expression in abs...

Over 200 unnatural amino acids of various chemical and physical properties have been genetically incorporated into proteins in E. coli, yeast and mammalian cells3. The unnatural amino acid is incorporated in response to a specific stop codon via an orthogonal engineered tRNA/synthetase pair. The genetical approach to modify proteins has provided valuable insights into protein structure and function. Here, we present a protocol for using Voltage-Clamp Fluorometry (VCF) in combination with a fluorescent UAA.
In VCF, the simultaneous observation of functional data and structural rearrangements localized around the fluorescent probe (~5 &#197;) allows us to obtain dynamic information with millisecond resolution1. The fluorescent probes alter their quenching state upon localized movement of the protein. A movement of only 1-2 &#197; is sufficient to lead to significant changes in the fluorescence intensity4. After identification of the site of interest in the target protein, the site is mutated by point mutation. Classically, the residue had been mutated to a cysteine whereas now, an amber stop codon (TAG) is introduced for genetic fUAA incorporation. The protein is then in vitro transcribed.
While other expression systems (e.g.,&#160;mammalian cells) can be used5,6,7, Xenopus oocytes are preferable for structure-function studies because of their larger size, leading to easier manipulation and higher fluorescence intensity (more fluorophores) and, therefore, to-noise ratio. Furthermore, Xenopus oocytes have low background from endogenous proteins2,8, and the dark pigmentation on the animal pole shields against background fluorescence from the cytosol. The Xenopus oocytes are surgically removed and DNA encoding the orthogonal tRNA/tRNA-synthetase pair specific for the fUAA is injected into the nucleus of the oocytes. After a 6-24 h incubation time, the protein RNA is co-injected with the fUAA into the cytosol of the oocytes, followed by a 2-3 days incubation period. In order to prevent any damage to the fUAA (photobleaching), the procedures including Anap have to be carried out under red light to avoid fluorophore excitation.
Oocytes are studied on a cut-open oocyte voltage-clamp setup, which is mounted on an upright fluorescence microscope, and electrical current and fluorescence changes are simultaneously recorded9,10. Alternatively, two-electrode voltage clamp1 or patch-clamp configurations11can be used. Fluorescence is excited by appropriate wavelengths with low RMS noise and emission recorded using a photodiode linked to an amplifier with high amplification.
There are several advantages of using fluorescent unnatural amino acids (fUAAs) in voltage-clamp fluorometry. One is access to the cytosolic side of the membrane proteins; many regulatory processes are located here (e.g., Ca2+- or nucleotide binding sites, fast and closed-state inactivation of voltage-gated ion channels, pore opening, module coupling). All these processes are now accessible for fluorescent labeling.
Another advantage is the small size of the probe leading to less disturbance of the protein. So far, two orthogonal tRNA/tRNA synthetase pairs for fUAAs have been engineered12,13, where 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap) is the only fUAA which has been used in Xenopus oocytes2,8. Anap is an environmentally sensitive fluorophore with a molecular weight of 272.3 g/mol and is only slightly bigger than tryptophan12 (Figures 1A, 1B). Due to its small size, fewer steric effects are likely to be introduced by the fluorophore compared to conventional fluorophores attached via a linker (typically more than 500 g/mol). Moreover, in the case of Anap, the fluorophore is located closer to the protein backbone than those linked to cysteines, and consequently, Anap is probing more localized rearrangements. Finally, removal of endogenous cysteines in conventional VCF in order to ensure site-specific labeling is no longer a requirement in UAA-VCF and therefore (i) leaves the proteins in (almost) their native state and (ii) allows VCF to be applied to study a wider range of proteins in which function may be altered by cysteine substitution.
<img alt="Figure 1" src="/files/ftp_upload/55598/55598fig1.jpg" /> 
Figure 1: Anap and Fluorescence Spectra. (A) Chemical structure of Anap. (B) Normalized absorption spectrum and emission spectra for 1 nM Anap, demonstrating the sensitivity of Anap fluorescence to the solvent hydrophobicity. Emission spectra were obtained by exciting at 350 nm. <a href="https://www.jove.com/files/ftp_upload/55598/55598fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
A disadvantage of using fluorescent UAAs is that a heterogeneous population of proteins may result from stop codon readthrough, translational reinitiation, C-terminal truncated proteins or crosstalk with endogenous aminoacylation if the amount of aminoacylated tRNAs is scarce. Such leak expression should always be checked for in the absence of the fUAA and the tRNA/tRNA synthetase pair. We addressed the issue of translational reinitiation and how to circumvent it for N-terminal insertion sites previously14. However, when the fUAA, tRNA and tRNA synthetase are present in saturated amounts, there only remains a low probability of leak expression.
The key procedural difference between fUAA-VCF and conventional VCF is the injection and handling of the oocytes; the injection of DNA encoding the tRNA and tRNA synthetase (pAnap) is followed by the introduction of Anap, which is either co-injected with the protein mRNA or alternatively added to the incubation solution as an acetoxymethyl (AM) ester.

<table border="0" cellpadding="0" cellspacing="0" width="567">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:199px;">Solutions</td>
			<td style="width:111px;"></td>
			<td style="width:161px;"></td>
			<td style="width:96px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Barth&#39;s solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NaCl&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>S7653</td>
			<td>90mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">KCl</td>
			<td>Fisher Scientific</td>
			<td>BP366-500</td>
			<td>3mM</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>M-9397</td>
			<td>0.82mM</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">CaCl2</td>
			<td>Sigma-Aldrich</td>
			<td>C-7902</td>
			<td>0.41mM</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Ca(NO3)2</td>
			<td>Sigma-Aldrich</td>
			<td>C-1396</td>
			<td>0.33mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034</td>
			<td>5mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NaOH hydrate</td>
			<td>BDH</td>
			<td>BDH7225-4</td>
			<td>pH 7.6</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicilin</td>
			<td>Invitrogen</td>
			<td>15140122</td>
			<td>100U/mL</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Streptomycin</td>
			<td>Invitrogen</td>
			<td>15140122</td>
			<td>100&#181;g/mL</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Kanamycin</td>
			<td>Invitrogen</td>
			<td>15160054</td>
			<td>10mg/100mL</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Horse serum</td>
			<td>Invitrogen</td>
			<td>16050122</td>
			<td>5%</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SOS Standard Oocyte Solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NaCl&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>746398</td>
			<td>102 mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">KCl</td>
			<td>Sigma-Aldrich</td>
			<td>746436</td>
			<td>3 mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MgCl2</td>
			<td>Sigma-Aldrich</td>
			<td>M9272</td>
			<td>1 mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034</td>
			<td>5 mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">External recording solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">N-methyl-D-glucamine (NMDG)</td>
			<td>Alfa Aesar</td>
			<td>L14282</td>
			<td>115mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034</td>
			<td>10mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Calcium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>239232</td>
			<td>2mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MES hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>258105</td>
			<td>pH 7.2</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Internal recording solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">N-methyl-D-glucamine (NMDG)</td>
			<td>Alfa Aesar</td>
			<td>L14282</td>
			<td>115mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034</td>
			<td>10mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ethylenediamine Tetraacetic Acid (EDTA)</td>
			<td>Fisher Scientific</td>
			<td>E478-500</td>
			<td>2mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MES hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>258105</td>
			<td>pH 7.2</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Labeling solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">KOH</td>
			<td>Fisher Scientific</td>
			<td>P250-1</td>
			<td>115mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034</td>
			<td>10mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Calcium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>239232</td>
			<td>2mM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MES hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>258105</td>
			<td>pH 7.2</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">TMR stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tetramethylrhodamine-5-maleimide (TMR)</td>
			<td>Molcular Probes by Life Technologies</td>
			<td>T6027</td>
			<td>5mM in DMSO</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Anap stock solution</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="80">
			<td height="80" style="height:80px;">Anap</td>
			<td>ABZENA (TCRS)</td>
			<td>Custom synthesis TCRS-170</td>
			<td style="width:96px;">1mM in nuclease-free water and 1% NaOH 1N</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Material/Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pAnap</td>
			<td>Addgene</td>
			<td>48696</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">High Performance Oocyte Clamp</td>
			<td>Dagan Corporation</td>
			<td>CA-1B</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gpatch Acquisition software</td>
			<td colspan="3">Department of Anesthesiology, University of California, Los Angeles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Analysis software</td>
			<td colspan="3">Department of Anesthesiology, University of California, Los Angeles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Recording Chamber</td>
			<td colspan="2">Custom machined</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Photo diode detection system</td>
			<td>Dagan Corporation</td>
			<td>PhotoMax-200/PIN</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Electrical shutter driver</td>
			<td>UNIBLITZ</td>
			<td>VCM-D1</td>
			<td></td>
		</tr>
	</tbody>
</table>

voltage-clamp fluorometry in xenopus oocytes using fluorescent unnatural amino acids

Voltage-Clamp Fluorometry (VCF) has been the technique of choice to investigate the structure and function of electrogenic membrane proteins where real-time measurements of fluorescence and currents simultaneously report on local rearrangements and global function, respectively1. While high-resolution structural techniques such as cryo-electron microscopy or X-ray crystallography provide static images of the proteins of interest, VCF provides dynamic structural data that allows us to link the structural rearrangements (fluorescence) to dynamic functional data (electrophysiology). Until recently, the thiol-reactive chemistry used for site-directed fluorescent labeling of the proteins restricted the scope of the approach because all accessible cysteines, including endogenous ones, will be labeled. It was thus required to construct proteins free of endogenous cysteines. Labeling was also restricted to sites accessible from the extracellular side. This changed with the use of Fluorescent Unnatural Amino Acids (fUAA) to specifically incorporate a small fluorescent probe in response to stop codon suppression using an orthogonal tRNA and tRNA synthetase pair2. The VCF improvement only requires a two-step injection procedure of DNA injection (tRNA/synthetase pair) followed by RNA/fUAA co-injection. Now, labelling both intracellular and buried sites is possible, and the use of VCF has expanded significantly. The VCF technique thereby becomes attractive for studying a wide range of proteins and &#8211; more importantly &#8211; allows investigating numerous cytosolic regulatory mechanisms.

Figure 4 shows an example of VCF recordings obtained from an oocyte expressing Shaker channels with fast inactivation removed (IR), L382stop-W434F in presence of pAnap and Anap. The W434F mutation blocks the ionic potassium currents, which makes it possible to measure the transient gating charge displacements (gating currents). The simultaneous recordings of gating currents (upper trace) and Anap fluorescence intensity changes (lower trace) upon depolarization demonstrate...

Watch this Scientific Journal Video about Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids at JoVE.com

Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids

This article describes an enhancement of conventional Voltage-Clamp Fluorometry (VCF) where Fluorescent Unnatural Amino Acids (fUAA) are used instead of maleimide dyes, to probe structural rearrangements in ion channels. The procedure includes Xenopus oocyte DNA injection, RNA/fUAA coinjection, and simultaneous current and fluorescence measurements.

Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids

Voltage-Clamp Fluorometry (VCF) has been the technique of choice to investigate the structure and function of electrogenic membrane proteins where ...

Research

JoVE Journal

Biochemistry

A Polyaniline-based Sensor of Nucleic Acids

Detection of nucleic acids is at the center of diagnostic technologies used in research and the clinic. Standard approaches used in these technologies ...

An Optimized Protocol for Electrophoretic Mobility Shift Assay Using Infrared Fluorescent Dye-labeled Oligonucleotides

Electrophoretic Mobility Shift Assays (EMSA) are an instrumental tool to characterize the interactions between proteins and their target DNA sequences. ...

Identification of Fatty Acids in Bacillus cereus

Identification of Fatty Acids in Bacillus cereus

The Bacillus species contain branched chain and unsaturated fatty acids (FAs) with diverse positions of the methyl branch (iso or anteiso) and of the ...

DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis

For any enzyme, robust, quantitative methods are required for characterization of both native and engineered enzymes. For DNA polymerases, DNA synthesis ...

Reconstitution of Cell-cycle Oscillations in Microemulsions of Cell-free Xenopus Egg Extracts

Reconstitution of Cell-cycle Oscillations in Microemulsions of Cell-free Xenopus Egg Extracts

Real-time measurement of oscillations at the single-cell level is important to uncover the mechanisms of biological clocks. Although bulk extracts ...

Structure Solution of the Fluorescent Protein Cerulean Using MeshAndCollect

X-ray crystallography is the major technique used to obtain high resolution information concerning the 3-dimensional structures of biological ...

Fluorescent Silver Staining of Proteins in Polyacrylamide Gels

Silver staining is a colorimetric technique widely used to visualize protein bands in polyacrylamide gels following sodium dodecyl sulfate-polyacrylamide ...

Single Liposome Measurements for the Study of Proton-Pumping Membrane Enzymes Using Electrochemistry and Fluorescent Microscopy

Proton-pumping enzymes of electron transfer chains couple redox reactions to proton translocation across the membrane, creating a proton-motive force used ...

Identifying Amino Acid Overproducers Using Rare-Codon-Rich Markers

To satisfy the ever-growing market for amino acids, high-performance production strains are needed. The amino acid overproducers are conventionally ...

Localization of SUMO-modified Proteins Using Fluorescent Sumo-trapping Proteins

Here we are presenting a novel method to study the sumoylation of proteins and their sub-cellular localization in mammalian cells and nematode oocytes. ...