Accommodation of a D-Phe residue into a right-handed 310-helix: Structure of Boc-D-Phe-(Aib)4-Gly-L-Leu-(Aib)2-Ome, an analogue of the amino terminal segment of antiamoebins and emerimicins
✍ Scribed by I. L. Karle; J. L Flippen-Anderson; K. Uma; P. Balaram
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1993
- Tongue
- English
- Weight
- 535 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
OMe (I), which is an analogue of the N-terminal sequence of antiamoebins and emerimicins, establishes a completely 3,0-helical conformation with seven successive intramolecular 4 + 1 hydrogen bonds. The average, 4,+ values for residues 1-8 are -59" and -32", respectively. Crystal parameters are C47H77NB012, space group P1, a = 10.636(4) A, b = 11.239(4) A, c = 12.227(6) A, a = 101.17(4)", B = 97.22(4)", y = 89.80(3)", Z = 1, R = 5.95% for 3018 data with I Fo I > 3a(F), resolution 0.93 A. The use of the torsion angle
, where K = 68" for D-Phe and K = 164' for L-Leu, confirms the opposite configurations of these residues. The q5,+ values of -62" and -32" at D-Phe are unusual, since this region is characteristic of residues with L configurations. Peptide I possesses only two chiral residues of opposing configuration. The observed right-handed 3,,-helical structure suggests that helix sense has probably been determined by the stereochemical preferences of the Leu residue.