The folding equilibrium of huntingtin exon 1 monomer depends on its polyglutamine tract

Bravo-Arredondo, Jose M.; Kegulian, Natalie C.; Schmidt, Thomas; Pandey, Nitin; Situ, Alan J.; Ulmer, Tobias S.; Langen, Ralf

doi:10.1074/jbc.ra118.004808

Cited by 42 publications

(60 citation statements)

References 52 publications

(68 reference statements)

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“…A number of in vitro experiments have established that the formation of fibrillar aggregates by proteins bearing polyQ tracts can proceed via oligomers 55 , potentially liquidlike 56 , stabilized by intermolecular interactions between flanking regions of polyQ tracts and equivalent to those stabilizing coiled coils 2,57,58 . In proteins bearing polyQ tracts such as huntingtin 59,60 and AR 20,21 extending the length of the tract increases its helicity and, as we have now shown, that of the sequence immediately flanking them at the Nterminus. Remarkably this also appears to be the case when they are studied in the context provided by the domains where they are found 20,21 and, indeed, in that provided by full length protein 60 .…”

Section: Discussionsupporting

confidence: 56%

“…Whether a certain change in tract length causes a decrease or an 14 28/02/2019 escobedo-topal18-ms for NPG -Google Docs https://docs.google.com/document/d/1WNpfN8MLwac98KPPAa_B_eK4TLUSgi-vjztLEuXS0IY/edit#heading=h.gjdgxs 15/22increase in activity might depend on whether the polyQ tract and its flanking regions are involved in interactions with transcriptional coactivators or corepressors and should therefore be contextdependent, as found experimentally 51,54 .A number of in vitro experiments have established that the formation of fibrillar aggregates by proteins bearing polyQ tracts can proceed via oligomers 55 , potentially liquidlike 56 , stabilized by intermolecular interactions between flanking regions of polyQ tracts and equivalent to those stabilizing coiled coils 2,57,58 . In proteins bearing polyQ tracts such as huntingtin 59,60 and AR 20,21 extending the length of the tract increases its helicity and, as we have now shown, that of the sequence immediately flanking them at the Nterminus. Remarkably this also appears to be the case when they are studied in the context provided by the domains where they are found 20,21 and, indeed, in that provided by full length protein 60 .…”

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confidence: 56%

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Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in the activation domain of a transcription factor

Escobedo¹,

Topal²,

Kunze³

et al. 2018

Preprint

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Polyglutamine (polyQ) tracts are regions of low sequence complexity of variable lengthfound in more than one hundred human proteins. These tracts are frequent in activation domains of transcription factors and their length often correlates with transcriptional activity. In addition, in nine proteins, tract elongation beyond specific thresholds causes polyQ disorders. To study the structural basis of the association between tract length, transcriptional activity and disease, here we addressed how the conformation of the polyQ tract of the androgen receptor (AR), a transcription factor associated with the polyQ disease spinobulbar muscular atrophy (SBMA), depends on its length. We found that the tract folds into a helical structure stabilized by unconventional hydrogen bonds between glutamine side chains and main chain carbonyl groups. These bonds are bifurcate with the conventional main chain to main chain hydrogen bonds stabilizing αhelices. In addition, since tract elongation provides additional interactions, the helicity of the polyQ tract directly correlates with its length. These findings suggest a plausible rationale for the association between polyQ tract length and AR transcriptional activity and have implications for establishing the mechanistic basis of SBMA.Polyglutamine (polyQ) tracts are lowcomplexity regions that are composed almost exclusively of Gln residues. They are frequent in the human proteome, particularly in the intrinsically disordered domains of proteins involved in the regulation of transcription, such as the activation domains of transcription factors 1 . The biological function of polyQ tracts is not wellunderstood, but it has been suggested that they regulate the activity of the proteins that harbor them by modulating the stability of the complexes that they form 2 . The lengths of polyQ tracts are variable because their coding DNA sequences tend to adopt secondary structures that hamper replication and repair 3 . Contractions and expansions in polyQ tracts can have functional consequences, and the lengths of the tracts may have been subject to natural selection 4 . As an example, it has been proposed that the length of the polyQ tract present in the protein huntingtin correlates with the intellectual coefficient 5 , presumably because it plays important although still not welldefined roles in neural plasticity 6 .For nine specific proteins, the variability in the lengths of polyQ tracts has pathogenic implications. Expansions beyond given thresholds are associated with nine rare hereditary neurodegenerative diseases known as polyQ diseases 7 . The mechanistic basis of this phenomenon is a matter of debate. Some authors have proposed that the expanded transcripts themselves are the neurotoxic species 8 due to their propensity to phase separate 9 , while others have suggested that expanded polyQ proteins are inherently neurotoxic 10 . However, it is widely believed that polyQ expansions cause neurotoxicity because they decrease protein solubility, which in turn leads to the formation of...

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Section: Discussionsupporting

confidence: 56%

supporting

confidence: 56%

Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in the activation domain of a transcription factor

Escobedo¹,

Topal²,

Kunze³

et al. 2018

Preprint

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“…The N-terminal htt NT sequence plays a critical role in facilitating aggregation and fibril formation of poly(Q) tracts within the Nterminal domain of huntingtin, encoded by exon 1 of the huntingtin gene (41). While previous investigations established that the htt NT sequence has helical propensity (18,(42)(43)(44), the initial events involved in htt NT multimerization that eventually lead to polyglutamine fibril nucleation and the structures of the multimers were unknown. Using a minimalistic construct, htt NT Q 7 , that remains predominantly monomeric over a sufficiently long period of time to enable detailed quantitative NMR measurements, but still eventually forms fibril, we were able to resolve at atomic resolution the early transient events in multimerization involving sparsely populated (<2%) oligomeric states, based on global analysis of the concentration dependence of an array of relaxation-based NMR measurements, including CPMG and R 1p relaxation dispersion, transverse relaxation in the rotating frame, and exchange-induced chemical shifts.…”

Section: Resultsmentioning

confidence: 99%

Probing initial transient oligomerization events facilitating Huntingtin fibril nucleation at atomic resolution by relaxation-based NMR

Kotler

Tugarinov

Schmidt

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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104

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The N-terminal region of the huntingtin protein, encoded by exon-1, comprises an amphiphilic domain (httNT), a polyglutamine (Qn) tract, and a proline-rich sequence. Polyglutamine expansion results in an aggregation-prone protein responsible for Huntington’s disease. Here, we study the earliest events involved in oligomerization of a minimalistic construct, httNTQ7, which remains largely monomeric over a sufficiently long period of time to permit detailed quantitative NMR analysis of the kinetics and structure of sparsely populated (≲2%) oligomeric states, yet still eventually forms fibrils. Global fitting of concentration-dependent relaxation dispersion, transverse relaxation in the rotating frame, and exchange-induced chemical shift data reveals a bifurcated assembly mechanism in which the NMR observable monomeric species either self-associates to form a productive dimer (τex ∼ 30 μs, Kdiss ∼ 0.1 M) that goes on to form a tetramer (τex≲25 μs; Kdiss ∼ 22 μM), or exchanges with a “nonproductive” dimer that does not oligomerize further (τex ∼ 400 μs; Kdiss ∼ 0.3 M). The excited state backbone chemical shifts are indicative of a contiguous helix (residues 3–17) in the productive dimer/tetramer, with only partial helical character in the nonproductive dimer. A structural model of the productive dimer/tetramer was obtained by simulated annealing driven by intermolecular paramagnetic relaxation enhancement data. The tetramer comprises a D2 symmetric dimer of dimers with largely hydrophobic packing between the helical subunits. The structural model, validated by EPR distance measurements, illuminates the role of the httNT domain in the earliest stages of prenucleation and oligomerization, before fibril formation.

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“…The N-terminal 17-residue sequence has been demonstrated to adopt a largely helical conformation when being membranes-associated (41,42,77,78), when part of a htt17-polyQ fiber (45,46,79) or in aggregation intermediates (51,73). Here we have shown that the membrane interactions of the htt17 flanking region of the polyQ domain promotes the aggregation process of huntingtin exon 1.…”

Section: Discussionmentioning

confidence: 61%

“…Recent structural investigations reveal a highly dynamic behaviour of htt17 and the subsequent polyQ domain where htt17 association (23), its interactions with the membrane (39)(40)(41)(42)(43) or with other polypeptide domains are associated with random coilhelix structural transitions (44,45). Interestingly, the htt17 and the polyQ domains mutually influence each other and their conformational properties are coupled (46,47).…”

mentioning

confidence: 99%

Membrane interactions accelerate the self-aggregation of huntingtin exon 1 fragments in a polyglutamine length-dependent manner

Marquette

Bechinger

2020

Preprint

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The accumulation of aggregated protein is a typical hallmark of many human neurodegenerative disorders including Huntington's disease. Misfolding of the amyloidogenic proteins gives rise to self-assembled complexes and fibers. The huntingtin protein is characterized by a segment of consecutive glutamines, which when exceeding a certain number of residues results in the occurrence of the disease.Furthermore, it has also been demonstrated that the 17-residue amino-terminal domain of the protein (htt17), located upstream of this polyglutamine tract, strongly correlates with aggregate formation and pathology. Here we demonstrate that membrane interactions strongly accelerate the oligomerization and β-amyloid fibril formation of htt17-polyglutamine segments. By using a combination of biophysical approaches the kinetics of fibre formation has been quantitatively investigated and found to be strongly dependent to the presence of lipids, the length of the polyQ expansion and the polypeptide-to-lipid ratio. Finally, the implications for therapeutic approaches are discussed. Statement of significance:The quantitative analysis of the aggregation kinetics of amino-terminal fragments of huntingtin demonstrate the importance of the 17residue amino-terminal membrane anchor and a resulting dominant effect of membranes in promoting the aggregation of polyglutamines. Other parameters further modulating the association kinetics are the length of the polyglutamine stretch and the peptide concentration. The findings can have important impact on finding new therapies to treat Huntington's and other polyglutamine related diseases.

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The folding equilibrium of huntingtin exon 1 monomer depends on its polyglutamine tract

Cited by 42 publications

References 52 publications

Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in the activation domain of a transcription factor

Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in the activation domain of a transcription factor

Probing initial transient oligomerization events facilitating Huntingtin fibril nucleation at atomic resolution by relaxation-based NMR

Membrane interactions accelerate the self-aggregation of huntingtin exon 1 fragments in a polyglutamine length-dependent manner

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