Theory of the helix-coil transition in single-chain polypeptides with interhelical contacts. The broken .alpha.-helical hairpin model

Content Provider	Semantic Scholar
Author	Skolnick, Jeffrey
Copyright Year	1985
Abstract	Because of the possible role of the a-helical hairpin in the early stages of globular protein folding, the theory of the helix-coil transition in single-chain polypeptides containing interhelical contacta originally developed by Poland and Scheraga (Biopolymers 1965,3,305) has been extended to encompass a broader range of accessible conformational states. In the "broken a-helical hairpin" model developed here, the individual polypeptide chain may possess a single pair of interacting helices, joined together by an interior random coil loop of variable length greater than or equal to some minimum value and where each interacting helix may perhaps have an appended tail containing alternating stretches of noninteracting helices and random coils. Expressions for the partition function, the overall helix content, the helix probability profiles, and the fraction of random coils in free-end random coil sequences and in the interior random coil loop between interacting helices have been developed for both the perfect matching limit where the molecule is essentially folded in half as well as the imperfect matching, out-of-register case in which any non-nearest-neighbor pair of a-helical turns is allowed to interact. The broken a-helical hairpin model has been applied to a hypothetical homo- polypeptide whose intrinsic helix content in the absence of interhelical contacts is small. The effect of the inclusion of out-of-register states on the breadth of the helix-coil transition of broken a-helical hairpins is investigated. Furthermore, a comparison of the helix-coil transition in a single-chain, broken a-helical hairpin and an analogous two-chain, coiled coil is made; the helix-coil transition in the former case is seen to be substantially sharper than in the latter case and reflects the enhanced cooperativity introduced by an interior random coil loop between interacting helices.
Starting Page	1073
Ending Page	1083
Page Count	11
File Format	PDF HTM / HTML
DOI	10.1021/ma00148a005
Alternate Webpage(s)	http://pwp.gatech.edu/cssb/wp-content/uploads/sites/385/2016/04/039-The-broken-helical-hairpin.pdf
Alternate Webpage(s)	http://cssb.biology.gatech.edu/skolnick/publications/pdffiles/039.pdf
Alternate Webpage(s)	https://doi.org/10.1021/ma00148a005
Volume Number	18
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article