Type II β-turn conformation of pivaloyl-L-prolyl-α-aminoisobutyryl-N-methylamide: Theoretical, spectroscopic, and X-ray studies

✍ Scribed by B. V. Venkataram Prasad; Hemalatha Balaram; P. Balaram

• Publisher: Wiley (John Wiley & Sons)
• Year: 1982
• Tongue: English
• Weight: 608 KB
• Volume: 21
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360210702

✦ Synopsis

Pivaloyl-L-Pro-Aib-N-methylamide has been shown to possess one intramolecular hydrogen bond in (CD&SO solution, by 'H-nmr methods, suggesting the existence of p-turns, with Pro-Aib as the corner residues. Theoretical conformational analysis suggests that Type I1 P-turn conformations are about 2 kcal mol-' more stable than Type 111 structures. A crystallographic study has established the Type I1 /%turn in the solid state. The molecule crystallizes in the space group P21 with a = 5.865 8, b = 11.421 A, c = 12.966 A, /3 = 97.55", and 2 = 2. The structure has been refined to a final R value of 0.061. The Type I1 p-turn conformation is stabilized by an intramolecular 4 -1 hydrogen bond between the methylamide NH and the pivaloyl CO group. The conformational angles are @pro = -57.8", $pro = 139.3', @Aib = 61.4', and $Ajb = 25.1'. The Type 11 /%turn conformation for Pro-Aib in this peptide is compared with the Type I11 structures observed for the same segment in larger peptides.