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Crystal structure of Boc‐Ala‐Aib‐Ala‐Aib‐Aib‐methyl ester, a pentapeptide fragment of the channel‐forming ionophore suzukacillin
Author(s) -
Francis A. K.,
Iqbal M.,
Balaram P.,
Vijayan M.
Publication year - 1983
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360220606
Subject(s) - pentapeptide repeat , chemistry , orthorhombic crystal system , hydrogen bond , molecule , crystal structure , crystallography , stereochemistry , helix (gastropod) , crystal (programming language) , peptide , organic chemistry , ecology , biochemistry , snail , biology , computer science , programming language
t ‐Buthyoxycarbonyl‐ L ‐alanyl‐α‐aminiosobutyryl‐ L ‐alanyl‐α‐aminoisobutyryl‐α‐aminoisobutyric acid methyl ester ( t ‐Boc‐ L ‐Ala‐Aib‐ L ‐Ala‐Aib‐Aib‐OMe), C 24 H 43 N 5 O 8 , an end‐protected pentapeptide with a sequence corresponding to the 6th through the 10th residues in suzukacillin, crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with a = 11.671, b = 14.534, c = 17.906 Å and z = 4. The molecule exists as a right‐handed 3 10 ‐helix with a pitch of 6.026 Å. The helix is stabilized by three 4 → 1 hydrogen bonds with the NH groups of Ala(3), Aib(4), and Aib(5) hydrogen bonding to the carbonyl oxygens of t ‐Boc, Ala(1), and Aib(2), respectively. The helical molecules arrange themselves in a head‐to‐tail fashion along the a direction in such a way that the NH groups of Ala(1) and Aib(2) hydrogen bond to the carbonyl oxygens of Aib(4) and Aib(5), respectively, of a translationally related molecule. The helical columns thus formed close‐pack nearly hexagonally to form the crystal.