%A Jesmita Dhar
%A Pinak Chakrabarti
%A Harpreet Saini
%A G.P.S. Raghava
%A Raghuvansh Kishore
%O Copyright of this article belongs to Wiley.
%J Proteins
%T ?-Turn: a novel ?-turn mimic in globular proteins stabilized by main-chain to side-chain C?H???O interaction.
%X Mimicry of structural motifs is a common feature in proteins. The 10-membered hydrogen-bonded ring involving the main-chain C ? O in a ?-turn can be formed using a side-chain carbonyl group leading to Asx-turn. We show that the N ? H component of hydrogen bond can be replaced by a C(?) -H group in the side chain, culminating in a nonconventional C ? H???O interaction. Because of its shape this ?-turn mimic is designated as ?-turn, which is found to occur ? three times per 100 residues. Three residues (i to i + 2) constitute the turn with the C ? H???O interaction occurring between the terminal residues, constraining the torsion angles ?i + 1, ?i + 1, ?i + 2 and ?'1(i + 2) (using the interacting C(?) atom). Based on these angles there are two types of ?-turns, each of which can be further divided into two groups. C(?) -branched side-chains, and Met and Gln have high propensities to occur at i + 2; for the last two residues the carbonyl oxygen may participate in an additional interaction involving the S and amino group, respectively. With Cys occupying the i + 1 position, such turns are found in the metal-binding sites. N-linked glycosylation occurs at the consensus pattern Asn-Xaa-Ser/Thr; with Thr at i + 2, the sequence can adopt the secondary structure of a ?-turn, which may be the recognition site for protein modification. Location between two ?-strands is the most common occurrence in protein tertiary structure, and being generally exposed ?-turn may constitute the antigenic determinant site. It is a stable scaffold and may be used in protein engineering and peptide design.
%N 2
%P 203-14
%V 83
%D 2015
%I Wiley
%L open1828