Role of histidine interruption in mitigating the pathological effects of long polyglutamine stretches in SCA1: A molecular approach

Abstract

Polyglutamine expansions, leading to aggregation, have been implicated in various neurodegenerative disorders. The range of repeats observed in normal individuals in most of these diseases is 19-36, whereas mutant proteins carry 40-81 repeats. In one such disorder, spinocerebellar ataxia (SCA1), it has been reported that certain individuals with expanded polyglutamine repeats in the disease range (Q 12 HQHQ 12 HQHQ 14/15 ) but with histidine interruptions were found to be phenotypically normal. To establish the role of histidine, a comparative study of conformational properties of model peptide sequences with (Q 12 HQHQ 12 HQHQ 12 ) and without (Q 42 ) interruptions is presented here. Q 12 HQHQ 12 HQHQ 12 displays greater solubility and lesser aggregation propensity compared to uninterrupted Q 42 as well as much shorter Q 22 . The solvent and temperature-driven conformational transitions (␤ structure ↔ random coil → ␣ helix) displayed by these model polyQ stretches is also discussed in the present report. The study strengthens our earlier hypothesis of the importance of histidine interruptions in mitigating the pathogenicity of expanded polyglutamine tract at the SCA1 locus. The relatively lower propensity for aggregation observed in case of histidine interrupted stretches even in the disease range suggests that at a very low concentration, the protein aggregation in normal cells, is possibly not initiated at all or the disease onset is significantly delayed. Our present study also reveals that besides histidine interruption, proline interruption in polyglutamine stretches can lower their aggregation propensity.

Pathogenic and Non-pathogenic Polyglutamine Tracts Have Similar Structural Properties: Towards a Length-dependent Toxicity Gradient

“…This result demonstrates the faster aggregation kinetics of Q41 when compared to Q22, in agreement with previous studies performed with synthetic polyQ peptides. 10,18 We also analysed the aggregation kinetics of cleaved Q41 and Q22 using a Coomassie blue staining SDS-PAGE method (Supplementary Data Figure S1c and d). This method confirms that Q41 peptides aggregate much faster than Q22 ones (at similar concentration), and shows in addition that the aggregation kinetic of Q22 depends on its concentration (Q22 (1.2 mM) aggregates faster than Q22 (0.2 mM)).…”

“…8,9,17 Likewise, circular dichroism (CD) experiments performed on synthetic polyQ peptides solubilized by treatment with strong acidic solvent used to destroy aggregates also revealed no structural difference between short and long polyQ. 10,18 To compound the debate, we have designed a simple strategy to produce concentrated polyQ peptides by specific cleavage from a glutathione-Stransferase (GST) carrier. This approach presents unique advantages over other strategies: it allows us to produce soluble polyQ in native-like conditions starting from a pure, well characterized and soluble protein, thus avoiding chemically synthesized peptides which, to be solubilized, need treatment with strong acidic solvents.…”

Phosphorylation-dependent Binding of 14-3-3 Proteins Controls TRESK Regulation

“…The (LEHQ 9 ) 9 polypeptide (approximating a random coil of 108 amino acids with a predicted contour length of about 41 nm) was designed on the basis of the known structure of polyglutamine peptides (20,21) and the N-terminal inactivation chain of Drosophila Shaker K ϩ channel (22). The coding regions of mouse TRESK and human 14-3-3 (the latter differs only in two amino acids from the mouse ortholog) were amplified by PCR from our pEXO-mTRESK clone (15) and pcDNA3.1-h14-3-3 (received from Andrey S. Shaw) with the mTRESK-s/mTRESK-a and h14-3-3-s/h14-3-3-a primer pairs, respectively.…”

Expansion, mosaicism and interruption: mechanisms of the CAG repeat mutation in spinocerebellar ataxia type 1

“…However, the observed circular dichroism spectra indicated that for both the short and long interrupted peptides, the β -sheets were intra-molecularly hydrogen bonded with the histidine residues found at the head of the hairpin. In contrast, the uninterrupted peptides adopted tightly linked, wide intermolecular β -sheets [48, 49]. Additional alkylation experiments determined that the histidine residues in the interrupted peptide aggregates are solvent-accessible, fitting with the previously proposed structural model [48, 49].…”

“…In an in vitro comparison of secondary structure conformation, aggregates of expanded and unexpanded versions of both interrupted and pure polyQ peptides adopted β -sheet conformation [48, 49]. However, the observed circular dichroism spectra indicated that for both the short and long interrupted peptides, the β -sheets were intra-molecularly hydrogen bonded with the histidine residues found at the head of the hairpin.…”