Abstract
The elongated three-helix‐bundle spectrin domains R16 and R17 fold and unfold unusually slowly over a rough energy landscape, in contrast to the homologue R15, which folds fast over a much smoother, more typical landscape. R15 folds via a nucleation–condensation mechanism that guides the docking of the A and C-helices. However, in R16 and R17, the secondary structure forms first and the two helices must then dock in the correct register. Here, we use variants of R16 and R17 to demonstrate that substitution of just five key residues is sufficient to alter the folding mechanism and reduce the landscape roughness. We suggest that, by providing access to an alternative, faster, folding route over their landscape, R16 and R17 can circumvent their slow, frustrated wild-type folding mechanism.
Highlights
Comparative folding studies combined with energy landscape theory have been applied successfully to the 15th, 16th and 17th repeats of chicken brain α-spectrin (R15, R16 and R17).[1,2,3,4,5,6,7] These domains are elongated three-helix bundles with a 106‐residue repeat length.[8,9,10,11] All three have similar structures, stabilities and Tanford β-values, but R16 and R17 fold and unfold some 3 orders of magnitude more slowly than R15.3,12 The folding landscapes of spectrin domains are complex
We have previously shown that comparisons of the Φ-values of the C-helix are the clearest indicator for different folding mechanisms in spectrin domains[4,6,7]; we wished to use a protein with an entirely wild type C-helix for
In helix C of R16m6(AB), the region of high Φ-values are those that pack onto the minimal core residues in the A‐helix (Fig. 6)
Summary
Comparative folding studies combined with energy landscape theory have been applied successfully to the 15th, 16th and 17th repeats of chicken brain α-spectrin (R15, R16 and R17).[1,2,3,4,5,6,7] These domains are elongated three-helix bundles with a 106‐residue repeat length.[8,9,10,11] All three have similar structures, stabilities and Tanford β-values, but R16 and R17 fold and unfold some 3 orders of magnitude more slowly than R15.3,12 The folding landscapes of spectrin domains are complex. We have previously shown that R16 and R17 are best described as folding on a landscape with a highenergy intermediate and that there are two consecutive transitions states, one early (TS1, rate limiting at low denaturant concentrations) and one late (TS2) (Fig. 1).[3,4,5,13] These slow-folding domains have been shown to have a rough energy landscape at TS1,. In contrast to R16 and R17, the early, rate determining TS (equivalent to TS1 in R16 and R17) over which R15 folds and unfolds appears to lack roughness.[7]. Energy landscape theory (introduced in the late 1980s) proposes that evolution has resulted in energy landscapes that are smooth, or unfrustrated (the principle of minimal frustration).[2] In particular, nonnative interactions are disfavored so that folding can proceed rapidly on a funnel-shaped free energy. TS1 TS2 can be diminished by providing an alternative folding pathway via a stable folding nucleus
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
