# Tuning the $\beta$-Turn Segment in Designed Peptide $\beta$-Hairpins: Construction a Stable Type I' $\beta$-Turn Nucleus and Hairpin-Helix Transition Promoting Segments

Rai, Rajkishor and Raghothama, Srinivasarao and Sridharan, Rajagopalan and Balaram, Padmanabhan (2006) Tuning the $\beta$-Turn Segment in Designed Peptide $\beta$-Hairpins: Construction a Stable Type I' $\beta$-Turn Nucleus and Hairpin-Helix Transition Promoting Segments. In: Biopolymers, 88 (3). pp. 350-361.

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## Abstract

Designed octapeptides Boc-Leu-Val-Val-Aib-$^DXxx$-Leu-Val-Val-OMe $(^DXxx=^DAla, 3a; ^DVal, 3c$ and $^DPro, 5a)$ and Boc-Leu-Phe-Val-Aib-$^DAla$-Leu-Phe-Val-OMe (3b) have been investigated to construct models of a stable type I' $\beta$-turn nucleated hairpin and to generate systems for investigating helix–hairpin conformational transitions. Peptide 5a, which contains a central $Aib-^D$ Pro segment, is shown to adopt a stable type I' $\beta$-turn nucleated hairpin structure, stabilized by four cross-strand hydrogen bonds. The stability of the structure in diverse solvents is established by the observation of all diagnostic NOEs expected in a $\beta$-hairpin conformation. Replacement of $^DPro5$ by $^DAla/^DVal (3a-c)$ results in sequences that form $\beta$-hairpins in hydrogen bonding solvents like $CD_3OH$ and $DMSO-d_6$. However, in $CDCl_3$ evidence for population of helical conformations is obtained. Peptide 6b (Boc-Leu-Phe-Val-Aib-Aib-Leu-Phe-Val-OMe), which contains a centrally positioned Aib-Aib segment, provides a clear example of a system, which exhibits a helical conformation in $CDCl_3$ and a significant population of both helices and hairpins in $CD_3OH$ and $DMSO-d_6$. The coexistence of multiple conformations is established by the simultaneous observation of diagnostic NOEs. Control over stereochemistry of the central $\beta$-turn permits generation of models for robust $\beta$-hairpins and also for the construction of systems that may be used to probe helix–hairpin conformational transitions.

Item Type: Journal Article Copyright of this article belongs to Wiley. Peptide b-turns;Peptide b-hairpins;Helix–hairpin conformational transition;NOEs Division of Biological Sciences > Molecular Biophysics Unit 05 Sep 2007 19 Sep 2010 04:39 http://eprints.iisc.ernet.in/id/eprint/11742