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Crystal structure and conformation of a cyclic tetrapeptide cyclo ( L ‐Pro‐Sar) 2 containing all‐ cis peptide units
Author(s) -
Ueno Katsuhiko,
Shimizu Toshimi
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.360220208
Subject(s) - tetrapeptide , chemistry , orthorhombic crystal system , crystal structure , crystallography , pyrrolidine , peptide , cyclic peptide , ring (chemistry) , crystal (programming language) , stereochemistry , biochemistry , organic chemistry , computer science , programming language
The crystal structure and conformation of the synthetic cyclic tetrapeptide, cyclo ( L ‐Pro‐Sar) 2 , was determined by x‐ray analysis. The peptide crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with cell parameters a = 9.277(1), b = 12.884(1), and c = 15.581(2) Å. The crystal structure was solved by the symbolic addition procedure for direct phase determination and least‐squares refinement using 1796 reflections, which led to the final R value of 0.043. This structure provides the first example observed in a crystal of a cyclic tetrapeptide in which all four peptide units have been found in the cis conformation with ω angles deviating slightly by 2°–10° from the ideal value of 0°. It was also found that the two Pro C α ‐CO single bonds assumed a trans ′ (ψ = 159.6° and 158.4°) conformation. Adjoining average planes of the peptide groups fall at nearly right angles to each other. The pyrrolidine ring conformations of the two prolyl residues are in the envelope form, with C γ carbon out of the least‐squares planes for the remaining four atoms.