Stabilization of two smallest possible diastereomeric β-hairpins in a water soluble tetrapeptide containing non-coded α-amino isobutyric acid (Aib) and m-amino benzoic acid
✍ Scribed by Anita Dutt; Arpita Dutta; Sudeshna Kar; Pradyot Koley; Michael G.B. Drew; Animesh Pramanik
- Publisher
- Elsevier Science
- Year
- 2009
- Tongue
- English
- Weight
- 521 KB
- Volume
- 928
- Category
- Article
- ISSN
- 0022-2860
No coin nor oath required. For personal study only.
✦ Synopsis
Single crystal X-ray diffraction study reveals that the water soluble tetrapeptide H 2 N-Ile-Aib-Leu-m-ABA-CO 2 H, containing non-coded Aib (a-amino isobutyric acid) and m-ABA (meta-amino benzoic acid), crystallizes with two smallest possible diastereomeric b-hairpin molecules in the asymmetric unit. Although in both of the molecules the chiralities at Ile(1) and Leu(3) are S, a conformational reversal in the back bone chain is observed to produce the b-hairpins with b-turn conformations of type II and II 0 . Interestingly Aib which is known to adopt helical conformation, adopts unusual semi-extended conformation with /: À49.5(5)°, w: 135.2(5)°in type II and /: 50.6(6)°, w: À137.0(4)°in type II 0 for occupying the i + 1 position of the b-turns. The two hairpin molecules are further interlocked through intermolecular hydrogen bonds and electrostatic interactions between -CO À 2 and À + NH 3 groups to form dimeric supramolecular b-hairpin aggregate in the crystal state. The CD measurement and 2D NMR study of the peptide in aqueous medium support the existence of b-hairpin structure in water.