This work was supported by the NIH (RO1-NS090390). We would also like to thank Dr. Joan Steffanfor technical assistance and discussion during the development of this assay.

Animal Ethics Statement - Experiments were carried out in strict accordance with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health and an approved animal research protocol by the Institutional Animal Care and Use Committee (IACUC) at the University of California, Irvine, an AAALAC accredited institution. All efforts were made to minimize animal suffering.
1. Preparation of Lysis Buffers
<ol>
	<li>Prepare &#34;Soluble&#34; lysis buffer (10 mM Tris pH 7.4, 1% Triton-X 100, 150 mM NaCl, 10% glycerol) and sterile filter through 0.22 &#181;m filter.
	<ol>
		<li>For a working &#34;Soluble&#34; lysis buffer, measure N-Ethylmaleimide (NEM) and thoroughly dissolve in 100 mM phenylmethysulfonyl&#160;flouride (PMSF) dissolved in 100% EtOH. 
		NOTE: Lysis Buffer Inhibitors: (i) 20 mM N-ethylmaleimide (NEM); (ii) 0.2 mM PMSF; (iii) 1 mM Sodium orthovanadate (Na3VO4); (iv) 1 &#181;g/mL leupeptin; (v) 1 &#181;g/mL aprotinin; (vi) 20 mM Sodium fluoride (NaF). 
		CAUTION: Wear a face mask when working with NEM throughout the protocol. Working lysis buffer must be made fresh to ensure active inhibitors.</li>
		<li>For soluble lysis buffer with protease inhibitors, add inhibitors in the following order: Sodium Fluoride (NaF), up to volume with cold lysis buffer, Sodium orthovanadate (Na3VO4), Aprotinin, and Leupeptin.</li>
	</ol>
	</li>
	<li>For &#34;Insoluble&#34; lysis buffer, supplement to 4% SDS by adding 500 &#181;L of 20% SDS to 2 mL of &#34;Soluble&#34; lysis buffer. Leave at room temperature. 
	NOTE: SDS will precipitate out when kept at 4 &#176;C ; keep this at room temp. Final Lysis Buffer composition: 10 mM Tris (pH 7.4); 1% Triton X-100; 150 mM NaCl; 10% glycerol; 4% SDS (Insoluble Only).</li>
</ol>
2. Soluble/Insoluble Fractionation Protocol
NOTE: See Figure 1 for a schematic.
<ol>
	<li>Label two sets of tubes for each sample: &#34;Soluble&#34; and &#34;Insoluble.&#34;</li>
	<li>Add X-&#181;L of ice-cold working soluble lysis buffer supplemented with protease inhibitors (see 1.1.1) to tissue. 
	NOTE: X = Volume varies depending on tissue amount; See Table 1.</li>
	<li>For mouse brain tissue (i.e., striatum), dounce slowly 30 times in glass 1 mL douncer&#160;and pipet into &#34;Insoluble&#34; labeled tube (keep on ice). 
	NOTE: Be careful not to break surface of liquid after starting douncing, as bubbles will form and may yield incomplete homogenization.</li>
	<li>For cells (i.e., HeLa, HEK293T), rinse cells once with cold, 1x PBS. Remove PBS and apply minimal volume of lysis buffer to cells and lift with cell scraper. 
	NOTE: For above cell lines, cells were plated at 5 x 105 cells per 6 well plate and grown to near confluency. One well is comparable to volumes used for mouse striatum.</li>
	<li>Transfer homogenate or cell lysate into labeled, &#34;Insoluble&#34; tubes and lyse on ice 1 h (Start clock after final tube is processed). 
	NOTE: For cell lysates, triturate several times to break up cell clumps prior to starting incubation. Avoid formation of bubbles. Briefly vortex pulse each sample for 1 s halfway through lysing.</li>
	<li>Centrifuge samples at 4 &#176;C at 15,000 x g for 20 min.</li>
	<li>Recover supernatant as the &#34;Soluble&#34; fraction.
	<ol>
		<li>Remove with pipet, be careful not to disturb pellet/cloudy layer as this will contaminate the fraction. Pipet soluble fraction into &#34;Soluble&#34; labeled tube. Keep on ice.</li>
	</ol>
	</li>
	<li>Wash pellet with 500 &#181;L of lysis buffer (x2) and centrifuge at 4 &#176;C at 15,000 x g for 5 min after each wash; it is okay if some of the cloudy layer is pipetted off.</li>
	<li>After final wash, remove ALL remaining wash buffer leaving only the tissue pellet. 
	NOTE: From this point, insoluble samples should now be kept at room temperature.</li>
	<li>Resuspend pellet with X-&#181;L lysis buffer supplemented with 4% SDS (Volume can be adjusted depending on pellet size; see Table 1).</li>
	<li>Sonicate each sample for 30 s at room temperature with a probe sonicator (125 Watts, 20 kHz, Pulse, Amplitude 40%, see Table of Materials).</li>
	<li>Boil samples (rolling boil) for 30 min; Centrifuge briefly (15 s) at 6,000 x g as to not lose any&#160;sample.</li>
	<li>Perform DC (detergent compatible) protein assay (see Table of Materials) or Lowry protein assay to measure protein concentration (recommended started dilutions of 1/5 of sample in respective lysis buffer for cell culture and 1/10 for tissue lysates). 
	NOTE: Protein concentrations will have to be read using a DC or Lowry assay due to high detergent concentration.</li>
	<li>Aliquot samples into 50 &#181;L batches to avoid freeze-thaw issues. 
	NOTE: Protocol can be paused here prior to further biochemical analysis by storing both fractions at -20 &#176;C.</li>
</ol>
3. Western Blot and Quantification
<ol>
	<li>Perform western blots as reported elsewhere1,13 by diluting 30 &#181;g of sample 1:1 in loading buffer (1.6x loading dye, 1x reducing). 
	NOTE: 30 &#181;g of protein per fraction is sufficient, but can be adjusted for optimal resolution. 3 - 8% Tris-Acetate poly-acrylamide gels should be used for the insoluble fraction. 4 - 12% Bis-Tris gels are recommended for the soluble fraction.</li>
	<li>Boil samples (rolling boil) for 5 min. Centrifuge briefly (15 s) at 6,000 x g to collect sample.</li>
	<li>Analyze fractions by SDS-PAGE and western blot, according to manufacturer&#39;s protocol for reduced samples. 
	NOTE: Insoluble fraction resolves best when transferred onto 0.45 &#181;M nitrocellulose membrane. 0.45 or 0.2 &#181;M nitrocellulose can be used for the soluble fraction, depending on the size of the protein of interest. Some optimization may be required for best transfer of HMW materials.</li>
	<li>Stain membrane with whole protein stain (e.g., MEMcode, see the Table of Materials) to visualize protein loading efficiency. 
	NOTE: Western blots can be analyzed by mean pixel intensity. Soluble fractions can be normalized to a house-keeping protein best suited for the experimental system. Insoluble fraction as relative protein abundance was verified by reversible protein staining or Histone 3 normalization on separate blot.</li>
</ol>

<ol>
	<li>Ochaba, 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=PIAS1+Regulates+Mutant+Huntingtin+Accumulation+and+Huntington's+Disease-Associated+Phenotypes+In+Vivo.">PIAS1 Regulates Mutant Huntingtin Accumulation and Huntington's Disease-Associated Phenotypes In Vivo.</a> Neuron. 90 (3), 507-520 (2016).</li><li>La Spada, A. R., Taylor, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repeat+expansion+disease:+progress+and+puzzles+in+disease+pathogenesis.">Repeat expansion disease: progress and puzzles in disease pathogenesis.</a> Nat Rev Genet. 11 (4), 247-258 (2010).</li><li>Reiner, A., Dragatsis, I., Dietrich, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetics+and+neuropathology+of+Huntington's+disease.">Genetics and neuropathology of Huntington's disease.</a> Int Rev Neurobiol. 98, 325-372 (2011).</li><li>The Huntington's Disease Collaborative Research Group. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+gene+containing+a+trinucleotide+repeat+that+is+expanded+and+unstable+on+Huntington's+disease+chromosomes.">A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington's disease chromosomes.</a> Cell. 72 (6), 971-983 (1993).</li><li>Sassone, J., Colciago, C., Cislaghi, G., Silani, V., Ciammola, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Huntington's+disease:+the+current+state+of+research+with+peripheral+tissues.">Huntington's disease: the current state of research with peripheral tissues.</a> Exp Neurol. 219 (2), 385-397 (2009).</li><li>Weydt, 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=Thermoregulatory+and+metabolic+defects+in+Huntington's+disease+transgenic+mice+implicate+PGC-1alpha+in+Huntington's+disease+neurodegeneration.">Thermoregulatory and metabolic defects in Huntington's disease transgenic mice implicate PGC-1alpha in Huntington's disease neurodegeneration.</a> Cell Metab. 4 (5), 349-362 (2006).</li><li>Schulte, J., Littleton, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+biological+function+of+the+Huntingtin+protein+and+its+relevance+to+Huntington's+Disease+pathology.">The biological function of the Huntingtin protein and its relevance to Huntington's Disease pathology.</a> Curr Trends Neurol. 5, 65-78 (2011).</li><li>Gipson, T. A., Neueder, A., Wexler, N. S., Bates, G. P., Housman, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aberrantly+spliced+HTT,+a+new+player+in+Huntington's+disease+pathogenesis.">Aberrantly spliced HTT, a new player in Huntington's disease pathogenesis.</a> RNA Biol. 10 (11), 1647-1652 (2013).</li><li>Neueder, A., 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=The+pathogenic+exon+1+HTT+protein+is+produced+by+incomplete+splicing+in+Huntington's+disease+patients.">The pathogenic exon 1 HTT protein is produced by incomplete splicing in Huntington's disease patients.</a> Sci Rep. 7 (1), 1307 (2017).</li><li>Arndt, J. R., Chaibva, M., Legleiter, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+emerging+role+of+the+first+17+amino+acids+of+huntingtin+in+Huntington's+disease.">The emerging role of the first 17 amino acids of huntingtin in Huntington's disease.</a> Biomol Concepts. 6 (1), 33-46 (2015).</li><li>Saudou, F., Finkbeiner, S., Devys, D., Greenberg, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Huntingtin+acts+in+the+nucleus+to+induce+apoptosis+but+death+does+not+correlate+with+the+formation+of+intranuclear+inclusions.">Huntingtin acts in the nucleus to induce apoptosis but death does not correlate with the formation of intranuclear inclusions.</a> Cell. 95 (1), 55-66 (1998).</li><li>Kim, S., Kim, K. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Therapeutic+Approaches+for+Inhibition+of+Protein+Aggregation+in+Huntington's+Disease.">Therapeutic Approaches for Inhibition of Protein Aggregation in Huntington's Disease.</a> Exp Neurobiol. 23 (1), 36-44 (2014).</li><li>O'Rourke, J. G., 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=SUMO-2+and+PIAS1+modulate+insoluble+mutant+huntingtin+protein+accumulation.">SUMO-2 and PIAS1 modulate insoluble mutant huntingtin protein accumulation.</a> Cell Rep. 4 (2), 362-375 (2013).</li><li>Shibata, 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=Regulation+of+intracellular+accumulation+of+mutant+Huntingtin+by+Beclin+1.">Regulation of intracellular accumulation of mutant Huntingtin by Beclin 1.</a> J Biol Chem. 281 (20), 14474-14485 (2006).</li><li>Apostol, B. L., 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+cell-based+assay+for+aggregation+inhibitors+as+therapeutics+of+polyglutamine-repeat+disease+and+validation+in+Drosophila.">A cell-based assay for aggregation inhibitors as therapeutics of polyglutamine-repeat disease and validation in Drosophila.</a> Proc Natl Acad Sci U S A. 100 (10), 5950-5955 (2003).</li><li>Wanker, E. E., 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=Membrane+filter+assay+for+detection+of+amyloid-like+polyglutamine-containing+protein+aggregates.">Membrane filter assay for detection of amyloid-like polyglutamine-containing protein aggregates.</a> Methods Enzymol. 309, 375-386 (1999).</li><li>Sontag, E. 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=Detection+of+Mutant+Huntingtin+Aggregation+Conformers+and+Modulation+of+SDS-Soluble+Fibrillar+Oligomers+by+Small+Molecules.">Detection of Mutant Huntingtin Aggregation Conformers and Modulation of SDS-Soluble Fibrillar Oligomers by Small Molecules.</a> J Huntingtons Dis. 1 (1), 119-132 (2012).</li><li>Grima, J. C., 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=Mutant+Huntingtin+Disrupts+the+Nuclear+Pore+Complex.">Mutant Huntingtin Disrupts the Nuclear Pore Complex.</a> Neuron. 94 (1), 93-107 (2017).</li><li>Sontag, E. 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=Methylene+blue+modulates+huntingtin+aggregation+intermediates+and+is+protective+in+Huntington's+disease+models.">Methylene blue modulates huntingtin aggregation intermediates and is protective in Huntington's disease models.</a> J Neurosci. 32 (32), 11109-11119 (2012).</li><li>Trushina, E., Rana, S., McMurray, C. T., Hua, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tricyclic+pyrone+compounds+prevent+aggregation+and+reverse+cellular+phenotypes+caused+by+expression+of+mutant+huntingtin+protein+in+striatal+neurons.">Tricyclic pyrone compounds prevent aggregation and reverse cellular phenotypes caused by expression of mutant huntingtin protein in striatal neurons.</a> BMC Neurosci. 10, 73 (2009).</li><li>Shahmoradian, S. H., 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=TRiC's+tricks+inhibit+huntingtin+aggregation.">TRiC's tricks inhibit huntingtin aggregation.</a> Elife. 2, e00710 (2013).</li><li>Kim, Y. 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=Proteasome+inhibition+induces+alpha-synuclein+SUMOylation+and+aggregate+formation.">Proteasome inhibition induces alpha-synuclein SUMOylation and aggregate formation.</a> J Neurol Sci. 307 (1-2), 157-161 (2011).</li><li>Goldberg, N. R. 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=Human+Neural+Progenitor+Transplantation+Rescues+Behavior+and+Reduces+alpha-Synuclein+in+a+Transgenic+Model+of+Dementia+with+Lewy+Bodies.">Human Neural Progenitor Transplantation Rescues Behavior and Reduces alpha-Synuclein in a Transgenic Model of Dementia with Lewy Bodies.</a> Stem Cells Transl Med. 6 (6), 1477-1490 (2017).</li></ol>

The authors have nothing to disclose.

Some precautions are needed for the above protocols to ensure consistent and quantitative results. First, mHTT in both fractions will spontaneously form aggregates over time upon multiple freeze thaw cycles, particularly when in a high concentration. It is thus critical to freeze aliquots of the protein preps, and thaw only the needed volume prior to running the assay as described in the protocol above. Further, if insoluble fraction yields white precipitant upon thawing, reconstitution may be necessary by an additional ...

The disruption of protein quality control networks that ensure proper folding and degradation of cellular proteins is likely central to pathology in Alzheimer&#39;s disease (AD), Parkinson&#39;s disease (PD), Huntington&#39;s disease (HD), and other &#34;protein misfolding&#34; disorders2,3. A detailed understanding of the proteostasis network components and their contributions to pathology are therefore crucial to developing improved therapeutic interventions. HD is caused by the abnormal expansion of a CAG repeat within the HD gene resulting in an expanded stretch of polyglutamines (polyQ) in the huntingtin (HTT) protein4. A consistent pathological feature of HD pathogenesis is the resulting misfolding, accumulation, and aggregation of HTT in regions of the brain and in peripheral tissues, which has been shown to interfere in several ways with normal cell homeostasis and function5,6. While HTT is ubiquitously expressed, medium spiny neurons in the striatum are selectively vulnerable and most overtly affected with notable cortical atrophy also associated with HD pathogenesis.
The formation of aggregates of HTT in the brain of HD patients and animal models has typically served as a proxy marker for disease progression and dominant-negative gain of function for mHTT7. Although the precise mechanisms by which protein misfolding and aggregation may contribute to mHTT-induced toxicity remain unclear, the formation of these inclusions in the brain of HD patients and various animal models is an invariant and inevitable feature. Inclusions appear to be comprised largely of accumulated HTT fragments containing the N-terminal expanded polyQ, indicating that proteolysis and processing of full-length HTT as well as alternative splicing8,9 may play an important role in the pathogenesis of HD. N-terminal HTT fragments may constitute a pathologic form of HTT that can aggregate rapidly, nucleate, and accelerate or propagate the aggregation process10.
However, the presence of these inclusions does not necessarily correlate with HTT-induced toxicity or cell death11. HTT has been proposed to undergo an aggregation process from a soluble monomer through soluble oligomeric species and &#946;-sheet fibrils to insoluble aggregates and inclusions12. Resolving these various protein species via standard biochemical assays has been a challenge in the field due to their stability in low-detergent lysis buffer and difficulty in visualizing using standard biochemical assays. Thus, methodological considerations are critical in detecting the degree and pattern of accumulated and aggregated mHTT.
The protocol presented here provides a method to visualize several intermediates of HTT, specifically the formation of an insoluble HMW HTT species that appears to closely track with HD pathogenesis and disease progression1,13,14. Being able to resolve and track multiple species of mHTT provides researchers a biochemical tool to study disease pathogenesis and evaluate potential therapeutic interventions through their modulation and impact on disease pathogenesis.

<table><tbody><tr><td>Sterile Filter</td><td>Millipore</td><td>SCGP505RE</td><td>Screw cap, sterile vaccum filter</td></tr><tr><td>1 mL Tissue Grinder, Dounce</td><td>Wheaton</td><td>357538</td><td></td></tr><tr><td>Sonicator</td><td>Qsonica</td><td>Model Q125</td><td></td></tr><tr><td>DC Protein Assay</td><td>Biorad</td><td>5000111</td><td>Comparable to Lowry assay</td></tr><tr><td>Tris 1M buffer solution</td><td>Alfa Aesar</td><td>J60636</td><td></td></tr><tr><td>Triton X-100</td><td>Fisher</td><td>BP151-100</td><td></td></tr><tr><td>NaCl 5M solution</td><td>Teknova</td><td>S0251</td><td></td></tr><tr><td>Glycerol</td><td>Fisher</td><td>BP229-1</td><td></td></tr><tr><td>20% SDS solution</td><td>Teknova</td><td>S0295</td><td></td></tr><tr><td>N-ethylmaleimide</td><td>Sigma</td><td>E1271</td><td></td></tr><tr><td>Phenylmethylsulfony flouride</td><td>Sigma</td><td>P7626</td><td>create 100mM stock solution in 100%EtOH, store at 4&amp;deg;C</td></tr><tr><td>Sodium orthovanadate</td><td>Sigma</td><td>S6508</td><td>Create 0.5M stock solution in water</td></tr><tr><td>Leupeptin</td><td>Sigma</td><td>L2884</td><td>Create 10mg/ml stock solution in water</td></tr><tr><td>Aprotinin</td><td>Sigma</td><td>A1153</td><td>Create 10mg/ml stock solution in water</td></tr><tr><td>Sodium Fluoride</td><td>Sigma</td><td>S4504</td><td>Create 500mM stock solution in water</td></tr><tr><td>Anti-HTT</td><td>Millipore</td><td>MAB5492</td><td>Use 1:1000 for western blot, 1:500 for filter retardation assay</td></tr><tr><td>Anti-GAPDH</td><td>Novus Biologicals</td><td>NB100-56875</td><td>Use 1:1000 for soluble western blot</td></tr></tbody></table>

fractionation for resolution of soluble and insoluble huntingtin species

The accumulation of misfolded proteins is central to pathology in Huntington's disease (HD) and many other neurodegenerative disorders. Specifically, a key pathological feature of HD is the aberrant accumulation of mutant HTT (mHTT) protein into high molecular weight complexes and intracellular inclusion bodies composed of fragments and other proteins. Conventional methods to measure and understand the contributions of various forms of mHTT-containing aggregates include fluorescence microscopy, western blot analysis, and filter trap assays. 
However, most of these methods are conformation specific, and therefore may not resolve the full state of mHTT protein flux due to the complex nature of aggregate solubility and resolution.
For the identification of aggregated mHTT and various modified forms and complexes, separation and solubilization of the cellular aggregates and fragments is mandatory. Here we describe a method to isolate and visualize soluble mHTT, monomers, oligomers, fragments, and an insoluble high molecular weight (HMW) accumulated mHTT species. HMW mHTT tracks with disease progression, corresponds with mouse behavior readouts, and has been beneficially modulated by certain therapeutic interventions1. This approach can be used with mouse brain, peripheral tissues, and cell culture but may be adapted to other model systems or disease contexts.

Resolution of soluble and insoluble cell lysates following fractionation can be detected using western analysis and filter retardation assays (Figure 2). As an example, HEK293T cells were transfected using transfection reagent (e.g., lipofectamine 2000), with HTT exon 1 encoding cDNA containing 97 glutamine repeats15 followed by the poly proline rich region, and these cells were allowed to express for 44 h. Cells were treated ...

Watch this Scientific Journal Video about Fractionation for Resolution of Soluble and Insoluble Huntingtin Species at JoVE.com

Fractionation for Resolution of Soluble and Insoluble Huntingtin Species

A method is described for fractionation of insoluble and soluble mutant huntingtin species from mouse brain and cell culture. The method described is useful for characterization and quantification of huntingtin protein flux and aids in analyzing protein homeostasis in disease pathogenesis and in the presence of perturbations

The accumulation of misfolded proteins is central to pathology in Huntington's disease (HD) and many other neurodegenerative disorders. Specifically, a ...

fractionation-for-resolution-soluble-insoluble-huntingtin

Research

JoVE Journal

Biochemistry

9.5K Views.  University of California Irvine. Een methode is beschreven voor fractionering van onoplosbare en oplosbare mutant huntingtin soorten van muis hersenen en cel cultuur. De beschreven methode is nuttig voor karakterisering en kwantificering van het huntingtin eiwit flux en aids in het analyseren van eiwitten homeostase in de pathogenese van de ziekte en in het bijzijn van verstoringen

Video: Fractionation for Resolution of Soluble and Insoluble Huntingtin Species

Brain Membrane Fractionation: An Ex Vivo Approach to Assess Subsynaptic Protein Localization

Assessing the synaptic protein composition and function constitutes an important challenge in neuroscience. However, it is not easy to evaluate neurotransmission that occurs within synapses because it is highly regulated by dynamic protein-protein interactions and phosphorylation events. Accordingly, when any method is used to study synaptic transmission, a major goal is to preserve these transient physiological modifications. Here, we present a brain membrane fractionation protocol that represents a robust procedure to isolate proteins belonging to different synaptic compartments. In other words, the protocol describes a biochemical methodology to carry out protein enrichment from presynaptic, postsynaptic, and extrasynaptic compartments. First, synaptosomes, or synaptic terminals, are obtained from neurons that contain all synaptic compartments by means of a discontinuous sucrose gradient. Of note, the quality of this initial synaptic membrane preparation is critical. Subsequently, the isolation of the different subsynaptic compartments is achieved with light solubilization using mild detergents at differential pH conditions. This allows for separation by gradient and isopycnic centrifugations. Finally, protein enrichment at the different subsynaptic compartments (i.e., pre-, post- and extrasynaptic membrane fractions) is validated by means of immunoblot analysis using well-characterized synaptic protein markers (i.e., SNAP-25, PSD-95, and synaptophysin, respectively), thus enabling a direct assessment of the synaptic distribution of any particular neuronal protein.

Brain Membrane Fractionation: An Ex Vivo Approach to Assess Subsynaptic Protein Localization

Here, we present a brain membrane fractionation protocol that represents a robust procedure to isolate proteins belonging to different synaptic compartments.

Assessing the synaptic protein composition and function constitutes an important challenge in neuroscience. However, it is not easy to evaluate ...

Enrichment of Detergent-insoluble Protein Aggregates from Human Postmortem Brain

In this study, we describe an abbreviated single-step fractionation protocol for the enrichment of detergent-insoluble protein aggregates from human postmortem brain. The ionic detergent N-lauryl-sarcosine (sarkosyl) effectively solubilizes natively folded proteins in brain tissue allowing the enrichment of detergent-insoluble protein aggregates from a wide range of neurodegenerative proteinopathies, such as Alzheimer&#39;s disease (AD), Parkinson&#39;s disease and amyotrophic lateral sclerosis, and prion diseases. Human control and AD postmortem brain tissues were homogenized and sedimented by ultracentrifugation in the presence of sarkosyl to enrich detergent-insoluble protein aggregates including pathologic phosphorylated tau, the core component of neurofibrillary tangles in AD. Western blotting demonstrated the differential solubility of aggregated phosphorylated-tau and the detergent-soluble protein, Early Endosome Antigen 1 (EEA1) in control and AD brain. Proteomic analysis also revealed enrichment of &#946;-amyloid (A&#946;), tau, snRNP70 (U1-70K), and apolipoprotein E (APOE) in the sarkosyl-insoluble fractions of AD brain compared to those of control, consistent with previous tissue fractionation strategies. Thus, this simple enrichment protocol is ideal for a wide range of experimental applications ranging from Western blotting and functional protein co-aggregation assays to mass spectrometry-based proteomics.

An abbreviated fractionation protocol for the enrichment of detergent-insoluble protein aggregates from human postmortem brain is described.

In this study, we describe an abbreviated single-step fractionation protocol for the enrichment of detergent-insoluble protein aggregates from human ...

Method for Efficient Refolding and Purification of Chemoreceptor Ligand Binding Domain

Identification of natural ligands of chemoreceptors and structural studies aimed at elucidation of the molecular basis of the ligand specificity can be greatly facilitated by the production of milligram amounts of pure, folded ligand binding domains. Attempts to heterologously express periplasmic ligand binding domains of bacterial chemoreceptors in Escherichia coli (E. coli) often result in their targeting into inclusion bodies. Here, a method is presented for protein recovery from inclusion bodies, its refolding and purification, using the periplasmic dCACHE ligand binding domain of Campylobacter jejuni (C. jejuni) chemoreceptor Tlp3 as an example. The approach involves expression of the protein of interest with a cleavable His6-tag, isolation and urea-mediated solubilisation of inclusion bodies, protein refolding by urea depletion, and purification by means of affinity chromatography, followed by tag removal and size-exclusion chromatography. The circular dichroism spectroscopy is used to confirm the folded state of the pure protein. It has been demonstrated that this protocol is generally useful for production of milligram amounts of dCACHE periplasmic ligand binding domains of other bacterial chemoreceptors in a soluble and crystallisable form.

A procedure is presented for the refolding of the dCACHE periplasmic ligand binding domain of Campylobacter jejuni chemoreceptor Tlp3 from inclusion bodies and the purification to yield milligram quantities of protein.

Identification of natural ligands of chemoreceptors and structural studies aimed at elucidation of the molecular basis of the ligand specificity can be ...

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, ...

Expression and Purification of the Human Lipid-sensitive Cation Channel TRPC3 for Structural Determination by Single-particle Cryo-electron Microscopy

Transient receptor potential channels (TRPCs) of the canonical TRP subfamily are nonselective cation channels that play an essential role in calcium homeostasis, particularly store-operated calcium entry, which is critical to maintaining proper function of synaptic vesicle release and intracellular signaling pathways. Accordingly, TRPC channels have been implicated in a variety of human diseases including cardiovascular disorders such as cardiac hypertrophy, neurodegenerative disorders such as Parkinson&#39;s disease, and neurologic disorders such as spinocerebellar ataxia. Therefore, TRPC channels represent a potential pharmacologic target in human diseases. However, the molecular mechanisms of gating in these channels are still unclear. The difficulty in obtaining large quantities of stable, homogeneous, and purified protein has been a limiting factor in structure determination studies, particularly for mammalian membrane proteins such as the TRPC ion channels. Here, we present a protocol for the large-scale expression of mammalian ion channel membrane proteins using a modified baculovirus gene transfer system and the purification of these proteins by affinity and size-exclusion chromatography. We further present a protocol to collect single-particle cryo-electron microscopy images from purified protein and to use these images to determine the protein structure. Structure determination is a powerful method for understanding the mechanisms of gating and function in ion channels.

This protocol describes techniques used to determine ion channel structures by cryo-electron microscopy, including a baculovirus system used to efficiently express genes in mammalian cells with minimum effort and toxicity, protein extraction, purification, and quality checking, sample grid preparation and screening, as well as data collection and processing.

Transient receptor potential channels (TRPCs) of the canonical TRP subfamily are nonselective cation channels that play an essential role in calcium ...

Expression, Purification, Crystallization, and Enzyme Assays of Fumarylacetoacetate Hydrolase Domain-Containing Proteins

Fumarylacetoacetate hydrolase (FAH) domain-containing proteins (FAHD) are identified members of the FAH superfamily in eukaryotes. Enzymes of this superfamily generally display multi-functionality, involving mainly hydrolase and decarboxylase mechanisms. This article presents a series of consecutive methods for the expression and purification of FAHD proteins, mainly FAHD protein 1 (FAHD1) orthologues among species (human, mouse, nematodes, plants, etc.). Covered methods are protein expression in E. coli, affinity chromatography, ion exchange chromatography, preparative and analytical gel filtration, crystallization, X-ray diffraction, and photometric assays. Concentrated protein of high levels of purity (&#62;98%) may be employed for crystallization or antibody production. Proteins of similar or lower quality may be employed in enzyme assays or used as antigens in detection systems (Western-Blot, ELISA). In the discussion of this work, the identified enzymatic mechanisms of FAHD1 are outlined to describe its hydrolase and decarboxylase bi-functionality in more detail.

Expression and purification of fumarylacetoacetate hydrolase domain-containing proteins is described with examples (expression in E. coli, FPLC). Purified proteins are used for crystallization and antibody production and employed for enzyme assays. Selected photometric assays are presented to display the multi-functionality of FAHD1 as oxaloacetate decarboxylase and acylpyruvate hydrolase.

Fumarylacetoacetate hydrolase (FAH) domain-containing proteins (FAHD) are identified members of the FAH superfamily in eukaryotes. Enzymes of this ...

Efficient and Scalable Production of Full-length Human Huntingtin Variants in Mammalian Cells using a Transient Expression System

Full-length huntingtin (FL HTT) is a large (aa 1-3,144), ubiquitously expressed, polyglutamine (polyQ)-containing protein with a mass of approximately 350 kDa. While the cellular function of FL HTT is not entirely understood, a mutant expansion of the polyQ tract above ~36 repeats is associated with Huntington's disease (HD), with the polyQ length correlating roughly with the age of onset. To better understand the effect of structure on the function of mutant HTT (mHTT), large quantities of the protein are required. Submilligram production of FL HTT in mammalian cells was achieved using doxycycline-inducible stable cell line expression. However, protein production from stable cell lines has limitations that can be overcome with transient transfection methods. 
This paper presents a robust method for low-milligram quantity production of FL HTT and its variants from codon-optimized plasmids by transient transfection using polyethylenimine (PEI). The method is scalable (&gt;10 mg) and consistently yields 1-2 mg/L of cell culture of highly purified FL HTT. Consistent with previous reports, the purified solution state of FL HTT was found to be highly dynamic; the protein has a propensity to form dimers and high-order oligomers. A key to slowing oligomer formation is working quickly to isolate the monomeric fractions from the dimeric and high-order oligomeric fractions during size exclusion chromatography. 
Size exclusion chromatography with multiangle light scattering (SEC-MALS) was used to analyze the dimer and higher-order oligomeric content of purified HTT. No correlation was observed between FL HTT polyQ length (Q23, Q48, and Q73) and oligomer content. The exon1-deleted construct (aa 91-3,144) showed comparable oligomerization propensity to FL HTT (aa 1-3,144). Production, purification, and characterization methods by SEC/MALS-refractive index (RI), sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), western blot, Native PAGE, and Blue Native PAGE are described herein.

We provide scalable protocols covering construct design, transient transfection, and expression and purification of full-length human huntingtin protein variants in HEK293 cells.

Full-length huntingtin (FL HTT) is a large (aa 1-3,144), ubiquitously expressed, polyglutamine (polyQ)-containing protein with a mass of approximately 350 ...

Extraction and Purification of FAHD1 Protein from Swine Kidney and Mouse Liver

Fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) is the first identified member of the FAH superfamily in eukaryotes, acting as oxaloacetate decarboxylase in mitochondria. This article presents a series of methods for the extraction and purification of FAHD1 from swine kidney and mouse liver. Covered methods are ionic exchange chromatography with fast protein liquid chromatography (FPLC), preparative and analytical gel filtration with FPLC, and proteomic approaches. After total protein extraction, ammonium sulfate precipitation and ionic exchange chromatography were explored, and FAHD1 was extracted via a sequential strategy using ionic exchange and size-exclusion chromatography. This representative approach may be adapted to other proteins of interest (expressed at significant levels) and modified for other tissues. Purified protein from tissue may support the development of high-quality antibodies, and/or potent and specific pharmacological inhibitors.

This protocol describes how to extract fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) from swine kidney and mouse liver. The listed methods may be adapted to other proteins of interest and modified for other tissues.

Fumarylacetoacetate hydrolase domain-containing protein 1 (FAHD1) is the first identified member of the FAH superfamily in eukaryotes, acting as ...

Purification of Hsp104, a Protein Disaggregase

Hsp104 is a hexameric AAA+ protein1 from yeast, which couples ATP hydrolysis to protein disaggregation2-10 (Fig. 1). This activity imparts two key selective advantages. First, renaturation of disordered aggregates by Hsp104 empowers yeast survival after various protein-misfolding stresses, including heat shock3,5,11,12. Second, remodeling of cross-beta amyloid fibrils by Hsp104 enables yeast to exploit myriad prions (infectious amyloids) as a reservoir of beneficial and heritable phenotypic variation13-22. Remarkably, Hsp104 directly remodels preamyloid oligomers and amyloid fibrils, including those comprised of the yeast prion proteins Sup35 and Ure223-30. This amyloid-remodeling functionality is a specialized facet of yeast Hsp104. The E. coli orthologue, ClpB, fails to remodel preamyloid oligomers or amyloid fibrils26,31,32.
Hsp104 orthologues are found in all kingdoms of life except, perplexingly, animals. Indeed, whether animal cells possess any enzymatic system that couples protein disaggregation to renaturation (rather than degradation) remains unknown33-35. Thus, we and others have proposed that Hsp104 might be developed as a therapeutic agent for various neurodegenerative diseases connected with the misfolding of specific proteins into toxic preamyloid oligomers and amyloid fibrils4,7,23,36-38. There are no treatments that directly target the aggregated species associated with these diseases. Yet, Hsp104 dissolves toxic oligomers and amyloid fibrils composed of alpha-synuclein, which are connected with Parkinson's Disease23 as well as amyloid forms of PrP39. Importantly, Hsp104 reduces protein aggregation and ameliorates neurodegeneration in rodent models of Parkinson's Disease23 and Huntington's disease38. Ideally, to optimize therapy and minimize side effects, Hsp104 would be engineered and potentiated to selectively remodel specific aggregates central to the disease in question4,7. However, the limited structural and mechanistic understanding of how Hsp104 disaggregates such a diverse repertoire of aggregated structures and unrelated proteins frustrates these endeavors30,40-42.
To understand the structure and mechanism of Hsp104, it is essential to study the pure protein and reconstitute its disaggregase activity with minimal components. Hsp104 is a 102kDa protein with a pI of ~5.3, which hexamerizes in the presence of ADP or ATP, or at high protein concentrations in the absence of nucleotide43-46. Here, we describe an optimized protocol for the purification of highly active, stable Hsp104 from E. coli. The use of E. coli allows simplified large-scale production and our method can be performed quickly and reliably for numerous Hsp104 variants. Our protocol increases Hsp104 purity and simplifies His6-tag removal compared to a previous purification method from E. coli47. Moreover, our protocol is more facile and convenient than two more recent protocols26,48.

Here, we describe a protocol for the purification of highly active Hsp104, a hexameric AAA+ protein from yeast, which couples ATP hydrolysis to protein disaggregation. This scheme exploits a His6-tagged construct for affinity purification from E. coli followed by anion-exchange chromatography, His6-tag removal with TEV protease, and size-exclusion chromatography.

Hsp104 is a hexameric AAA+ protein1 from yeast, which couples ATP hydrolysis to protein disaggregation2-10 (Fig. 1). This activity imparts two key ...

Biology

Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells

Rapid responses involving fast redistribution of messenger(m)RNA and alterations of mRNA translation are pertinent to ongoing homeostatic adjustments of the cells. These adjustments are critical to eukaryotic cell survivability and &#39;damage control&#39; during fluctuating nutrient and salinity levels, temperature, and various chemical and radiation stresses. Due to the highly dynamic nature of the RNA-level responses, and the instability of many of the RNA:RNA and RNA:protein intermediates, obtaining a meaningful snapshot of the cytoplasmic RNA state is only possible with a limited number of methods. Transcriptome-wide, RNA-seq-based ribosome profiling-type experiments are among the most informative sources of data for the control of translation. However, absence of a uniform RNA and RNA:protein intermediate stabilization can lead to different biases, particularly in the fast-paced cellular response pathways. In this article, we provide a detailed protocol of rapid fixation applicable to eukaryotic cells of different permeability, to aid in RNA and RNA:protein intermediate stabilization. We further provide examples of isolation of the stabilized RNA:protein complexes based on their co-sedimentation with ribosomal and poly(ribo)somal fractions. The separated stabilized material can be subsequently used as part of ribosome profiling-type experiments, such as in Translation Complex Profile sequencing (TCP-seq) approach and its derivatives. Versatility of the TCP-seq-style methods has now been demonstrated by the applications in a variety of organisms and cell types. The stabilized complexes can also be additionally affinity-purified and imaged using electron microscopy, separated into different poly(ribo)somal fractions and subjected to RNA sequencing, owing to the ease of the crosslink reversal. Therefore, methods based on snap-chilling and formaldehyde fixation, followed by the sedimentation-based or other type of RNA:protein complex enrichment, can be of particular interest in investigating finer details of rapid RNA:protein complex dynamics in live cells.

Rapid In Vivo Fixation and Isolation of Translational Complexes from Eukaryotic Cells

We present a technique to rapidly stabilize translational (protein biosynthesis) complexes with formaldehyde crosslinking in live yeast and mammalian cells. The approach enables dissecting transient intermediates and dynamic RNA:protein interactions. The crosslinked complexes can be used in multiple downstream applications such as in deep sequencing-based profiling methods, microscopy, and mass-spectrometry.

Rapid responses involving fast redistribution of messenger(m)RNA and alterations of mRNA translation are pertinent to ongoing homeostatic adjustments of ...

Fractionation for Resolution of Soluble and Insoluble Huntingtin Species

Samenvatting

Meer video's verkennen