Dataset Information

Structural transition from helices to hemihelices.

ABSTRACT: Helices are amongst the most common structures in nature and in some cases, such as tethered plant tendrils, a more complex but related shape, the hemihelix forms. In its simplest form it consists of two helices of opposite chirality joined by a perversion. A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section. Our findings provides the basis for the deterministic manufacture of a variety of complex three-dimensional shapes from flat strips.

SUBMITTER: Liu J

PROVIDER: S-EPMC3997338 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Structural transition from helices to hemihelices.

Liu Jia J Huang Jiangshui J Su Tianxiang T Bertoldi Katia K Clarke David R DR

PloS one 20140423 4

Helices are amongst the most common structures in nature and in some cases, such as tethered plant tendrils, a more complex but related shape, the hemihelix forms. In its simplest form it consists of two helices of opposite chirality joined by a perversion. A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transiti ...[more]

PMID: 24759785

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Project description:OGlcNAcylation and phosphorylation are the major competing intracellular post-translational modifications of serine and threonine residues. The structural effects of both post-translational modifications on serine and threonine were examined within Baldwin model α-helical peptides (Ac-AKAAAAKAAAAKAAGY-NH2 or Ac-YGAKAAAAKAAAAKAA-NH2). At the N-terminus of an α-helix, both phosphorylation and OGlcNAcylation stabilized the α-helix relative to the free hydroxyls, with a larger induced structure for phosphorylation than for OGlcNAcylation, for the dianionic phosphate than for the monoanionic phosphate, and for modifications on threonine than for modifications on serine. Both phosphoserine and phosphothreonine resulted in peptides more α-helical than alanine at the N-terminus, with dianionic phosphothreonine the most α-helix-stabilizing residue here. In contrast, in the interior of the α-helix, both post-translational modifications were destabilizing with respect to the α-helix, with the greatest destabilization seen for threonine OGlcNAcylation at residue 5 and threonine phosphorylation at residue 10, with peptides containing either post-translational modification existing as random coils. At the C-terminus, both OGlcNAcylation and phosphorylation were destabilizing with respect to the α-helix, though the induced structural changes were less than in the interior of the α-helix. In general, the structural effects of modifications on threonine were greater than the effects on serine, because of both the lower α-helical propensity of Thr and the more defined induced structures upon modification of threonine than serine, suggesting threonine residues are particularly important loci for structural effects of post-translational modifications. The effects of serine and threonine post-translational modifications are analogous to the effects of proline on α-helices, with the effects of phosphothreonine being greater than those of proline throughout the α-helix. These results provide a basis for understanding the context-dependent structural effects of these competing protein post-translational modifications.

Project description:It is established that prion protein is the sole causative agent in a number of diseases in humans and animals. However, the nature of conformational changes that the normal cellular form, PrP(C), undergoes in its conversion to a self-replicating state is still not fully understood. The ordered C-terminus of PrP(C) proteins has three helices (H1-H3). Here, we use statistical coupling analysis (SCA) to infer covariations at various locations using a family of evolutionarily related sequences and the response of mouse and human PrP(C)s to mechanical force to decipher the initiation sites for the transition from PrP(C) to an aggregation-prone PrP* state. Sequence-based SCA predicts that the clustered residues in nonmammals are localized in the stable core (near H1) of PrP(C), whereas in mammalian PrP(C), they are localized in frustrated helices H2 and H3 where most of the pathogenic mutations are found. Force-extension curves and free energy profiles as a function of extension of mouse and human PrP(C) in the absence of a disulfide (SS) bond between residues Cys179 and Cys214, generated by applying mechanical force to the ends of the molecule, show a sequence of unfolding events starting first with rupture of H2 and H3. This is followed by disruption of structure in two strands. Helix H1, stabilized by three salt bridges, resists substantial force before unfolding. Force extension profiles and the dynamics of rupture of tertiary contacts also show that even in the presence of an SS bond the instabilities in most of H3 and parts of H2 still determine the propensity to form the PrP* state. In mouse PrP(C) with an SS bond, there are ?10 residues that retain their order even at high forces. Both SCA and single-molecule force simulations show that in the conversion from PrP(C) to PrP(SC) major conformational changes occur (at least initially) in H2 and H3, which because of their sequence compositions are frustrated in the helical state. Implications of our findings for the structural model for the scrapie form of PrP(C) are discussed.

Dataset Information

Structural transition from helices to hemihelices.

Publications

Structural transition from helices to hemihelices.

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