Name: interactions with and membrane permeabilization of brain mitochondria by amyloid fibrils
Uploaded: 2019-09-28T14:00:00
Description: Watch this Scientific Journal Video about Interactions with and Membrane Permeabilization of Brain Mitochondria by Amyloid Fibrils at JoVE.com

This work was supported by grants from the Research Council of the Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran.

All animal experiments were performed in accordance with the Institutional Animal Care and Use Committee (IACUC) of Medical Sciences of Tehran University. Maximal efforts were made to minimize suffering and detrimental effects to the rats by sharpening the guillotine blades and applying resolute and swift movements of the blade.
1. Brain homogenization and mitochondrial isolation
NOTE: All reagents for mitochondrial isolation were prepared according to Sims and Anders...

<ol>
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A wealth of experimental results supports the hypothesis that the cytotoxicity of fibrillar aggregates is significantly associated with their ability to interact with and permeabilize biological membranes4,5. However, most of the data are based on artificial lipid bilayers that do not necessarily reflect the intrinsic properties of biological membranes, which are heterogeneous structures with a wide variety of phospholipids and proteins. Here, using brain mitocho...

Amyloid-related disorders, known as amyloidoses, constitute a large group of diseases defined by the appearance of insoluble protein deposits in different tissues and organs1,2. Among them, neurodegenerative disorders are the most frequently forms in which protein aggregates appear in the central or peripheral nervous system2. Although a number of mechanisms have been proposed to be involved in the toxicity of amyloid aggregates3, a growing body of evidence points to cell membrane disruption and permeabilization as the primary mechanism of amyloid pathology4,5. In addition to plasma membrane, internal organelles (i.e., mitochondria) may also be affected.
Interestingly, emerging evidence suggests that mitochondrial dysfunction plays a critical role in the pathogenesis of neurodegenerative disorders, including Alzheimer&#8217;s and Parkinson&#8217;s diseases6,7. In accordance with this issue, numerous reports have indicated binding and accumulation of amyloid &#946;-peptide, &#945;-synuclein, Huntingtin, and ALS-linked mutant SOD1 proteins to mitochondria8,9,10,11. The mechanism of membrane permeabilization by amyloid aggregates is thought to occur either through formation of discrete channels (pores) and/or through a nonspecific detergent-like mechanism5,12,13. It is noteworthy that most of these conclusions have been based on reports involving phospholipid model systems, and studies directly targeting the events occurring in biological membranes are rare. Clearly, these artificial lipid bilayers do not necessarily reflect the intrinsic properties of&#160;biological membranes, including those of mitochondria, which are heterogeneous structures and composed of a wide variety of phospholipids and proteins.
In the present study, mitochondria isolated from rat brains are used as an in vitro biological model to examine the destructive effects of amyloid fibrils arising from &#945;-synuclein (as an amyloidogenic protein), bovine insulin (as a model peptide showing significant structural homology with human insulin involved in injection-localized amyloidosis), and hen egg white lysozyme (HEWL; as a common model protein for study of amyloid aggregation). The interactions and possible damage of mitochondrial membranes induced by amyloid fibrils are then investigated by observing the release of mitochondrial malate dehydrogenase (MDH) (located in the mitochondrial matrix) and mitochondria reactive oxygen species (ROS) enhancement.

<table>
	<tbody>
		<tr>
			<td>2&#8242;,7&#8242;-Dichlorodihydrofluorescein diacetate</td>
			<td>Sigma</td>
			<td>35845</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium sulfate</td>
			<td>Merck</td>
			<td>1012171000</td>
			<td></td>
		</tr>
		<tr>
			<td>Black 96-well plate</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Black Clear-bottomed 96-well plate</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine insulin</td>
			<td>Sigma</td>
			<td>I6634</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Sigma</td>
			<td>A2153</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA essentially fatty acid-free</td>
			<td>Sigma</td>
			<td>A6003</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Sigma</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Crystal clear sealing tape</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CuSO4</td>
			<td>Sigma</td>
			<td>451657</td>
			<td></td>
		</tr>
		<tr>
			<td>Dialysis bag (cut off 2 KDa)</td>
			<td>Sigma</td>
			<td>D2272</td>
			<td></td>
		</tr>
		<tr>
			<td>Dounce homogenizer</td>
			<td>Potter Elvehjem</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma</td>
			<td>E9884</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence plate reader</td>
			<td>BioTek</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence spectrophotometer</td>
			<td>Cary Eclipse VARIAN</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Folin</td>
			<td>Merck</td>
			<td>F9252</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma</td>
			<td>G7126</td>
			<td></td>
		</tr>
		<tr>
			<td>Guillotine</td>
			<td>Made in Iran</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>HCl</td>
			<td>Merck</td>
			<td>H1758</td>
			<td></td>
		</tr>
		<tr>
			<td>Hen Egg White Lysozyme (HEWL)</td>
			<td>Sigma</td>
			<td>L6876</td>
			<td></td>
		</tr>
		<tr>
			<td>Na2CO3</td>
			<td>Sigma</td>
			<td>S7795</td>
			<td></td>
		</tr>
		<tr>
			<td>NaH2PO4</td>
			<td>Sigma</td>
			<td>S7907</td>
			<td></td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Merck</td>
			<td>S8045</td>
			<td></td>
		</tr>
		<tr>
			<td>Oxaloacetate</td>
			<td>Sigma</td>
			<td>O4126</td>
			<td></td>
		</tr>
		<tr>
			<td>Percoll</td>
			<td>GE Healthcare</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffer Saline (PBS)</td>
			<td>Sigma</td>
			<td>CS0030</td>
			<td></td>
		</tr>
		<tr>
			<td>PMSF</td>
			<td>Sigma</td>
			<td>P7626</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium sodium tartrate</td>
			<td>Sigma</td>
			<td>217255</td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz cuvette</td>
			<td>Sigma</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrophotometer</td>
			<td>analytik jena</td>
			<td>SPEKOL 2000 model</td>
			<td></td>
		</tr>
		<tr>
			<td>Succinate</td>
			<td>Sigma</td>
			<td>S2378</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Merck</td>
			<td>1076871000</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermomixer</td>
			<td>Eppendorph</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Thioflavin T</td>
			<td>Sigma</td>
			<td>T3516</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-HCl</td>
			<td>Merck</td>
			<td>1082191000</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma</td>
			<td>T9284</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptone</td>
			<td>QUELAB</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>Memmert</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast Extract</td>
			<td>QUELAB</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#946;-NADH</td>
			<td>Sigma</td>
			<td>N8129</td>
			<td></td>
		</tr>
	</tbody>
</table>

interactions with and membrane permeabilization of brain mitochondria by amyloid fibrils

A growing body of evidence indicates that membrane permeabilization, including internal membranes such as mitochondria, is a common feature and primary mechanism of amyloid aggregate-induced toxicity in neurodegenerative diseases. However, most reports describing the mechanisms of membrane disruption are based on phospholipid model systems, and studies directly targeting events occurring at the level of biological membranes are rare. Described here is a model for studying the mechanisms of amyloid toxicity at the membrane level. For mitochondrial isolation, density gradient medium is used to obtain preparations with minimal myelin contamination. After mitochondrial membrane integrity confirmation, the interaction of amyloid fibrils arising from &#945;-synuclein, bovine insulin, and hen egg white lysozyme (HEWL) with rat brain mitochondria, as an in vitro biological model, is investigated. The results demonstrate that treatment of brain mitochondria with fibrillar assemblies can cause different degrees of membrane permeabilization and ROS content enhancement. This indicates structure-dependent interactions between amyloid fibrils and mitochondrial membrane. It is suggested that biophysical properties of amyloid fibrils and their specific binding to mitochondrial membranes may provide explanations for some of these observations.

The protocol describes a model for studying the interactions of amyloid fibril with rat brain mitochondria as an in vitro biological model. For mitochondrial preparation, 15% (v/v) density gradient medium was used to remove myelin as major contamination of brain tissue14. As shown in Figure 1A, centrifugation at 30,700 x g produced two distinct bands of material, myelin (as the major component of band 1) and band 2, which...

Watch this Scientific Journal Video about Interactions with and Membrane Permeabilization of Brain Mitochondria by Amyloid Fibrils at JoVE.com

Interactions with and Membrane Permeabilization of Brain Mitochondria by Amyloid Fibrils

Provided here is a protocol for investigating the interactions between native form, prefibrillar, and mature amyloid fibrils of different peptides and proteins with mitochondria isolated from different tissues and various areas of the brain.

A growing body of evidence indicates that membrane permeabilization, including internal membranes such as mitochondria, is a common feature and primary ...

In this video, we describe a model study for the mechanism of amyloid toxicity at the membrane level using rat brain mitochondria as an in vitro biological model. Despite accumulating report describing mechanism of membrane perturbations by amyloid aggregate in phospholipid model systems studied directly targeting the events beginning at developing biological membrane. In the present video, we describe amyloid fibrils of alpha-synuclein analyzing the rat brain mitochondria membrane as an in vitro biological model.We believe that mitochondria as an organelle with well-characterized membranes may provide an extremely useful biological model system for molecular studies related to the mechanism of amyloid cytotoxicity at the membrane level relating to neurodegenerative diseases. Decapitate the rat with a small animal guillotine and remove the brain from the scale within one minute of the decapitation of the rat to limit possible deterioration of mitochondrial properties. It is important to work quickly and keep everything on ice throughout the procedure.Wash the tissue twice with 30 milliliter of isolation buffer. Transfer to a beaker containing cold isolation buffer and finely mince the brain with scissors. Transfer the tissue suspension to a 20 milliliter cold dounce homogenizer.Homogenize the tissue pieces using nine up and down strokes with a motorized pestle. Leave the mixture on ice for approximately 30 seconds after each set of three homogenization strokes to ensure the homogenate remains cold. Transfer the homogenate to a pre-chilled centrifuge tube and centrifuge at 1, 300 G at four Centigrade for three minutes.Carefully decant the supernatant and transfer it to a pre-chilled centrifuge tube. Centrifuge at 21, 000 G at four Centigrade for 10 minutes. Discard the supernatant and resuspend the pellet in a density gradient medium by gently stirring the mixture with the pipette.Centrifuge in a fixed angle rotor at 30, 700 G at four Centigrade for five minutes. Using a Pasteur pipette, remove the sharp end of material accumulated at the top, which mostly contain myelin. Add eight milliliter isolation buffer to the mitochondrial fraction while gently stirring the mixture with the pipette.Centrifuge at 16, 700 G at four Centigrade for 10 minutes. Carefully remove the supernatant, leaving the bottom loose pellet undisturbed. Add one milliliter 10 milligram per milliliter fatty acid-free BSA to centrifuge tube while gently stirring the mixture with the tip of the pipette.Make up the volume to five milliliter by adding isolation buffer. Centrifuge at 6, 900 G at four Centigrade for 10 minutes. This should produce a firm pellet.Decant the supernatant and gently resuspend the mitochondrial pellet in isolation buffer. Dilute mitochondrial homogenate to one milligram per milliliter with cold isolation buffer and place in two 1.5 milliliter tubes, typically 195 microliter of mitochondria per tube. Add five microliter 20%volume per volume Triton X-100 to one tube as positive control for maximum enzyme activity and five microliter deionized water to another tube for control, followed by mixing with a stirrer.Incubate the tubes for 10 minutes in warm water bath set to 30 Centigrade. Pellet mitochondria by centrifugation of tubes in a fixed angle rotor at 16, 000 G four Centigrade for 15 minutes. Carefully collect resulting supernatants for assessing the activity of mitochondrial malate dehydrogenase using a standard spectrophotometric assay described on the next part.Calculate the integrity of mitochondrial membrane as follows. For malate dehydrogenase activity determination, pipette 890 and 880 microliter 50 millimolar Tris-HCL buffer to blank and sample test cuvettes respectively followed by 100 microliter 50 millimolar oxaloacetate and 10 microliter of 10 millimolar beta-NADH. Put the cuvettes in a spectrophotometer and reference against blank.Add 10 microliter mitochondrial homogenate one milligram per milliliter to sample cuvette. Immediately mix by inversion. Record decrease in absorbance due to NADH oxidation at 340 nanometer for one minute.For alpha-synuclein amyloid fibrillation, add 294 microliter of protein solution, 200 micromolar to each 1.5 milliliter tube. Then add six microliter ThT solution one millimolar. Mix the solutions and incubate the tubes in a thermomixer at 37 Centigrade under constant stirring at 800 RPM.For bovine insulin amyloid fibrillation, add 637 microliter of protein solution, 250 micromolar to 1.5 milliliter tube. Then add 13 microliter ThT solution one millimolar followed by stirring. Add aliquots 200 microliter of protein solutions to each well of a clear bottom 96-well plate.Seal the plate with crystal clear sealing tape. Load the plate into Cytation 5 fluorescence plate reader. Measure ThT fluorescence at 30-minute intervals for 12 hours.Use excitation at 440 nanometer and emission at 485 nanometer. Select the wells. Shake the plate for five seconds before each measurement.Set the temperature at 57 Centigrade without agitation. Prepare two series of 1.5 milliliter tubes containing mitochondrial homogenates, one series for MDH release assay and other for mitochondrial ROS measurement. Add aliquots of fresh or amyloid fibrils of alpha-synuclein, bovine insulin or hen egg white lysozyme to mitochondrial homogenate followed by gently pipetting.Incubate tubes containing mitochondrial suspensions for 30 minutes in warm water bath set to 30 Centigrade. For malate dehydrogenase release assay, centrifuge incubated mitochondrial homogenates at 16, 000 G for 15 minutes. Carefully collect resulting supernatants for assaying the activity of mitochondrial MDH as described on protocol section part four.Calculate the release of MDH as follows. For mitochondrial ROS measurement, pipette 191 microliter of incubated mitochondrial homogenate to each well of a 96-well plate. Add four microliter of 50 micromolar DCFDA.Then add five microliter of 200 millimolar succinate. Incubate the plate for 30 minutes in warm water bath set to 30 Centigrade while gently stirring. Load the plate into a Cytation 5 fluorescence plate reader and measure fluorescence intensity according to the protocol section.Mitochondrial membrane integrity was assessed by measuring MDH activity in the isolated mitochondria before and after membrane disruption and enzyme release by Triton X-100. As you see, we typically found that mitochondrial preparations are about 93%intact. ThT fluorescence assay was carried out to monitor growth of amyloid fibrils.The curve for amyloid fibrillation of three proteins showed a typical sigmoidal pattern, reaching to a plateau at about 96, 12, and 96 hours for alpha-synuclein, bovine insulin, and hen egg white lysozyme respectively, suggesting formation of amyloid fibrils that was more confirmed by AFM measurement. Possible permeabilization and damage of mitochondrial membrane by amyloid fibrils was investigated by the release of mitochondrial MDH and mitochondrial ROS measurement. As you see in the left graph, substantial release of MDH was observed upon addition of the alpha-synuclein amyloid fibrils to mitochondria.While a slight release was detected by insulin fibrils, hen egg white lysozyme fibrils were found to be ineffective. Right graph shows the effect of amyloid fibrils on mitochondrial ROS content. While no significant enhancement in mitochondrial ROS was observed upon addition of hen egg white lysozyme or insulin amyloid fibrils, treatment with alpha-synuclein fibrils led to a considerable increase in ROS content of brain mitochondria.The present video describes a model study for the mechanism of fibula aggregate cytotoxicity at the membrane level, demonstrating how amyloid fibrils arising from various proteins may cause different degrees of membrane damage and permeabilization. While some topics of amyloid fibrils and their specific binding membrane appear to provide with the capacity to interact with and cause destabilization and subsequent perturbations of membranes. After this video, you will be able to investigate the interaction of native form, pre-fibrillar, and mature amyloid fibrils of different peptides and with mitochondria isolated from different tissues or various areas of the brain.

interactions-with-membrane-permeabilization-brain-mitochondria

Research

JoVE Journal

Biochemistry

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

Method to Visualize and Analyze Membrane Interacting Proteins by Transmission Electron Microscopy

Monotopic proteins exert their function when attached to a membrane surface, and such interactions depend on the specific lipid composition and on the availability of enough area to perform the function. Nanodiscs are used to provide a membrane surface of controlled size and lipid content. In the absence of bound extrinsic proteins, sodium phosphotungstate-stained nanodiscs appear as stacks of coins when viewed from the side by transmission electron microscopy (TEM). This protocol is therefore designed to intentionally promote stacking; consequently, the prevention of stacking can be interpreted as the binding of the membrane-binding protein to the nanodisc. In a further step, the TEM images of the protein-nanodisc complexes can be processed with standard single-particle methods to yield low-resolution structures as a basis for higher resolution cryoEM work. Furthermore, the nanodiscs provide samples suitable for either TEM or non-denaturing gel electrophoresis. To illustrate the method, Ca2+-induced binding of 5-lipoxygenase on nanodiscs is presented.

Many proteins perform their function when attached to membrane surfaces. The binding of extrinsic proteins on nanodisc membranes can be indirectly imaged by transmission electron microscopy. We show that the characteristic stacking (rouleau) of nanodiscs induced by the negative stain sodium phosphotungstate is prevented by the binding of extrinsic protein.

Monotopic proteins exert their function when attached to a membrane surface, and such interactions depend on the specific lipid composition and on the ...

A Tailored HPLC Purification Protocol That Yields High-purity Amyloid Beta 42 and Amyloid Beta 40 Peptides, Capable of Oligomer Formation

Amyloidogenic peptides such as the Alzheimer's disease-implicated Amyloid beta (A&#946;), can present a significant challenge when trying to obtain high purity material. Here we present a tailored HPLC purification protocol to produce high-purity amyloid beta 42 (A&#946;42) and amyloid beta 40 (A&#946;40) peptides. We have found that the combination of commercially available hydrophobic poly(styrene/divinylbenzene) stationary phase, polymer laboratory reverse phase - styrenedivinylbenzene (PLRP-S) under high pH conditions, enables the attainment of high purity (&gt;95%) A&#946;42 in a single chromatographic run. The purification is highly reproducible and can be amended to both semi-preparative and analytical conditions depending upon the amount of material wished to be purified. The protocol can also be applied to the A&#946;40 peptide with identical success and without the need to alter the method.

Herein we report a tailored HPLC purification protocol that yields high-purity amyloid beta 42 (A&#946;42) and amyloid beta 40 (A&#946;40) peptides, capable of oligomer formation. Amyloid beta is a highly aggregation prone, hydrophobic peptide implicated in Alzheimer&#39;s disease. The amyloidogenic nature of the peptide makes its purification a challenge.

Amyloidogenic peptides such as the Alzheimer's disease-implicated Amyloid beta (A&#946;), can present a significant challenge when trying to obtain high ...

Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging

Proteins that deposit as amyloid in tissues throughout the body can be the cause or consequence of a large number of diseases. Among these we find neurodegenerative diseases such as Alzheimer&#39;s and Parkinson&#39;s disease afflicting primarily the central nervous system, and systemic amyloidosis where serum amyloid A, transthyretin and IgG light chains deposit as amyloid in liver, carpal tunnel, spleen, kidney, heart, and other peripheral tissues. Amyloid has been known and studied for more than a century, often using amyloid specific dyes such as Congo red and Thioflavin T (ThT) or Thioflavin (ThS). In this paper, we present heptamer-formyl thiophene acetic acid (hFTAA) as an example of recently developed complements to these dyes called luminescent conjugated oligothiophenes (LCOs). hFTAA is easy to use and is compatible with co-staining in immunofluorescence or with other cellular markers. Extensive research has proven that hFTAA detects a wider range of disease associated protein aggregates than conventional amyloid dyes. In addition, hFTAA can also be applied for optical assignment of distinct aggregated morphotypes to allow studies of amyloid fibril polymorphism. While the imaging methodology applied is optional, we here demonstrate hyperspectral imaging (HIS), laser scanning confocal microscopy and fluorescence lifetime imaging (FLIM). These examples show some of the imaging techniques where LCOs can be used as tools to gain more detailed knowledge of the formation and structural properties of amyloids. An important limitation to the technique is, as for all conventional optical microscopy techniques, the requirement for microscopic size of aggregates to allow detection. Furthermore, the aggregate should comprise a repetitive &#946;-sheet structure to allow for hFTAA binding. Excessive fixation and/or epitope exposure that modify the aggregate structure or conformation can render poor hFTAA binding and hence pose limitations to accurate imaging.

Amyloid deposition is a hallmark of different diseases and afflicts many different organs. This paper describes the application of luminescent conjugated oligothiophene fluorescence staining in combination with fluorescence microscopy techniques. This staining method represents a powerful tool for detection and exploration of protein aggregates in both clinical and scientific setups.

Proteins that deposit as amyloid in tissues throughout the body can be the cause or consequence of a large number of diseases. Among these we find ...

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 ...

Detection of Detergent-sensitive Interactions Between Membrane Proteins

Our ability to explore protein-protein interactions is the key to understanding regulatory connections in the cell. However, detection of protein-protein interactions in many cases is associated with significant experimental challenges. In particular, sorting receptors interact with their protein cargo in the lumen of the membrane compartments often in a detergent-sensitive fashion, making co-immunoprecipitation of these proteins unusable. Binding of the sorting receptor sortilin to glucose transporter GLUT4 may serve as an example of weak luminal interactions between membrane proteins. Here, we describe a fast, simple, and inexpensive assay to validate the interaction between sortilin and GLUT4. For that, we have designed and chemically synthesized the myc-tagged peptide corresponding to the potential sortilin-binding epitope in the luminal part of GLUT4. Sortilin tagged with six histidines was expressed in mammalian cells, and isolated from cell lysates using Cobalt beads. Sortilin immobilized on the beads was incubated with the peptide solution at different pH values, and the eluted material was analyzed by Western blotting. This assay can be easily adapted to study other detergent-sensitive protein-protein interactions.

We describe a protocol for detection of detergent-sensitive interactions between membrane proteins using binding of the sorting receptor, sortilin, to the first luminal loop of the glucose transporter protein, GLUT4, as an example.

Our ability to explore protein-protein interactions is the key to understanding regulatory connections in the cell. However, detection of protein-protein ...

Generation of Native, Untagged Huntingtin Exon1 Monomer and Fibrils Using a SUMO Fusion Strategy

Huntington&#39;s Disease (HD) is an inherited fatal neurodegenerative disease caused by a CAG expansion (&#8805;36) in the first exon of the HD gene, resulting in the expression of the Huntingtin protein (Htt) or N-terminal fragments thereof with an expanded polyglutamine (polyQ) stretch.
The exon1 of the Huntingtin protein (Httex1) is the smallest Htt fragment that recapitulates many of the features of HD in cellular and animal models and is one of the most widely studied fragments of Htt. The small size of Httex1 makes it experimentally more amenable to biophysical characterization using standard and high-resolution techniques in comparison to longer fragments or full-length Htt. However, the high aggregation propensity of mutant Httex1 (mHttex1) with increased polyQ content (&#8805;42) has made it difficult to develop efficient expression and purification systems to produce these proteins in sufficient quantities and make them accessible to scientists from different disciplines without the use of fusion proteins or other strategies that alter the native sequence of the protein. We present here a robust and optimized method for the production of milligram quantities of native, tag-free Httex1 based on the transient fusion of small ubiquitin related modifier (SUMO). The simplicity and efficiency of the strategy will eliminate the need to use non-native sequences of Httex1, thus making this protein more accessible to researchers and improving the reproducibility of experiments across different laboratories. We believe that these advances will also facilitate future studies aimed at elucidating the structure-function relationship of Htt as well as developing novel diagnostic tools and therapies to treat or slow the progression of HD.

Here, we present a robust and optimized protocol for the production of milligram quantities of native, tag-free monomers and fibrils of the exon1 of the Huntingtin protein (Httex1) based on the transient fusion of small ubiquitin related modifier (SUMO).

Huntington&#39;s Disease (HD) is an inherited fatal neurodegenerative disease caused by a CAG expansion (&#8805;36) in the first exon of the HD gene, ...

Measuring Trans-Plasma Membrane Electron Transport by C2C12 Myotubes

Trans-plasma membrane electron transport (tPMET) plays a role in protection of cells from intracellular reductive stress as well as protection from damage by extracellular oxidants. This process of transporting electrons from intracellular reductants to extracellular oxidants is not well defined. Here we present spectrophotometric assays by C2C12 myotubes to monitor tPMET utilizing the extracellular electron acceptors: water-soluble tetrazolium salt-1 (WST-1) and 2,6-dichlorophenolindophenol (DPIP or DCIP). Through reduction of these electron acceptors, we are able to monitor this process in a real-time analysis. With the addition of enzymes such as ascorbate oxidase (AO) and superoxide dismutase (SOD) to the assays, we can determine which portion of tPMET is due to ascorbate export or superoxide production, respectively. While WST-1 was shown to produce stable results with low background, DPIP was able to be re-oxidized after the addition of AO and SOD, which was demonstrated with spectrophotometric analysis. This method demonstrates a real-time, multi-well, quick spectrophotometric assay with advantages over other methods used to monitor tPMET, such as ferricyanide (FeCN) and ferricytochrome c reduction.

The goal of this protocol is to spectrophotometrically monitor trans-plasma membrane electron transport utilizing extracellular electron acceptors and to analyze enzymatic interactions that may occur with these extracellular electron acceptors.

Trans-plasma membrane electron transport (tPMET) plays a role in protection of cells from intracellular reductive stress as well as protection from damage ...

Analysis of &#946;-Amyloid-induced Abnormalities on Fibrin Clot Structure by Spectroscopy and Scanning Electron Microscopy

This article presents methods for generating in vitro fibrin clots and analyzing the effect of beta-amyloid (A&#946;) protein on clot formation and structure by spectrometry and scanning electron microscopy (SEM). A&#946;, which forms neurotoxic amyloid aggregates in Alzheimer&#39;s disease (AD), has been shown to interact with fibrinogen. This A&#946;-fibrinogen interaction makes the fibrin clot structurally abnormal and resistant to fibrinolysis. A&#946;-induced abnormalities in fibrin clotting may also contribute to cerebrovascular aspects of the AD pathology such as microinfarcts, inflammation, as well as, cerebral amyloid angiopathy (CAA). Given the potentially critical role of neurovascular deficits in AD pathology, developing compounds which can inhibit or lessen the A&#946;-fibrinogen interaction has promising therapeutic value. In vitro methods by which fibrin clot formation can be easily and systematically assessed are potentially useful tools for developing therapeutic compounds. Presented here is an optimized protocol for in vitro generation of the fibrin clot, as well as analysis of the effect of A&#946; and A&#946;-fibrinogen interaction inhibitors. The clot turbidity assay is rapid, highly reproducible and can be used to test multiple conditions simultaneously, allowing for the screening of large numbers of A&#946;-fibrinogen inhibitors. Hit compounds from this screening can be further evaluated for their ability to ameliorate A&#946;-induced structural abnormalities of the fibrin clot architecture using SEM. The effectiveness of these optimized protocols is demonstrated here using TDI-2760, a recently identified A&#946;-fibrinogen interaction inhibitor.

Analysis of &amp;#946;-Amyloid-induced Abnormalities on Fibrin Clot Structure by Spectroscopy and Scanning Electron Microscopy

Presented here are two methods that can be used individually or in combination to analyze the effect of beta-amyloid on fibrin clot structure. Included is a protocol for creating an in vitro fibrin clot, followed by clot turbidity and scanning electron microscopy methods.

This article presents methods for generating in vitro fibrin clots and analyzing the effect of beta-amyloid (A&#946;) protein on clot formation and ...

A Fluorescence Fluctuation Spectroscopy Assay of Protein-Protein Interactions at Cell-Cell Contacts

A variety of biological processes involves cell-cell interactions, typically mediated by proteins that interact at the interface between neighboring cells. Of interest, only few assays are capable of specifically probing such interactions directly in living cells. Here, we present an assay to measure the binding of proteins expressed at the surfaces of neighboring cells, at cell-cell contacts. This assay consists of two steps: mixing of cells expressing the proteins of interest fused to different fluorescent proteins, followed by fluorescence fluctuation spectroscopy measurements at cell-cell contacts using a confocal laser scanning microscope. We demonstrate the feasibility of this assay in a biologically relevant context by measuring the interactions of the amyloid precursor-like protein 1 (APLP1) across cell-cell junctions. We provide detailed protocols on the data acquisition using fluorescence-based techniques (scanning fluorescence cross-correlation spectroscopy, cross-correlation number and brightness analysis) and the required instrument calibrations. Further, we discuss critical steps in the data analysis and how to identify and correct external, spurious signal variations, such as those due to photobleaching or cell movement.
In general, the presented assay is applicable to any homo- or heterotypic protein-protein interaction at cell-cell contacts, between cells of the same or different types and can be implemented on a commercial confocal laser scanning microscope. An important requirement is the stability of the system, which needs to be sufficient to probe diffusive dynamics of the proteins of interest over several minutes.

This protocol describes a fluorescence fluctuation spectroscopy-based approach to investigate interactions among proteins mediating cell-cell interactions, i.e. proteins localized in cell junctions, directly in living cells. We provide detailed guidelines on instrument calibration, data acquisition and analysis, including corrections to possible artefact sources.

A variety of biological processes involves cell-cell interactions, typically mediated by proteins that interact at the interface between neighboring ...