Conformational interconversions in peptide β-turns: Discrimination between enantiomeric conformations by chiral perturbation
✍ Scribed by S. Raghothama; Manjula Chaddha; S. Banumathi; Krishnan Ravikumar; D. Velmurugan; P. Balaram
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1998
- Tongue
- English
- Weight
- 213 KB
- Volume
- 45
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The crystal structure of the model tripeptide Boc-Aib-Gly-Leu-OMe (1) reveals two independent molecules in the asymmetric unit that adopt ''enantiomeric'' type I and type I b-turn conformations with the Aib and Gly residues occupying the corner (i / 1 and i / 2) positions. 13 C cross polarization and magic angle sample spinning spectra in the solid state also support the coexistence of two conformational species. 13 C-nmr in CDCl 3 establishes the presence of a single species or rapid exchange between conformations. 400 MHz 1 H-nmr provides evidence for conformational exchange involving a major and minor species, with b- turn conformations supported by the low solvent exposure of Leu(3) NH and the observation of N i H } N i/1 H nuclear Overhauser effects. CD bands in the region 190-230 nm are positive, supporting a major population of type I b-turns. The isomeric peptide, Boc-Gly-Leu-Aib-OMe (2), adopts an ''open'' type II b-turn conformation in crystals. Solid state and solution nmr support population of a single conformational species. Chiral perturbation introduced outside the folded region of peptides may provide a means of modulating screw sense in achiral sequences.