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Structure and conformation of the calcium complex of cyclo(Ala-Leu-Pro-Gly)2 in two crystal forms

Jois, DS and Prasad, GS and Bednarek, M and Easwaran, KR and Vijayan, M (1993) Structure and conformation of the calcium complex of cyclo(Ala-Leu-Pro-Gly)2 in two crystal forms. In: International Journal of Peptide & Protein Research, 41 (5). pp. 484-491.

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1399-...

Abstract

Crystal structures of two different forms of the calcium perchlorate complex of cyclo(Ala-Leu-Pro-Gly)2 have been determined and refined using X-ray crystallographic techniques. Orthorhombic form: C32H52N8O8.Ca(ClO4)2.7H2O.2CH3OH, space group C222(1), a = 14.366, b = 18.653, c = 19.824 A, Z = 4, R = 0.068 for 2208 observed reflections. Monoclinic form: C32H52N8O8.Ca(ClO4)2.4H2O, space group C2, a = 21.096, b = 10.182, c = 11.256 A, beta = 103.33 degrees, Z = 2, R = 0.075 for 2165 observed reflections. The cyclic peptide molecule in both the structures has the form of a twofold symmetric, slightly elongated bowl. Type II' beta-turns, involving Gly and Ala at the corners, exist at the two ends of the molecule. The interior of the molecule is substantially hydrophilic, and the external surface of the bowl is largely hydrophobic. The calcium ion is located at the centre of the mouth of the bowl-like molecule. In both crystal forms, four peptide carbonyl oxygens from the cyclic peptide and two solvent oxygens coordinate to the metal ion. The mode of complexation may be described as incomplete encapsulation as, for example, in the case of metal complexes of antamanide. In the crystal structures the complex ions are held together by hydrogen bonds involving perchlorate ions and water molecules. The molecular structure observed in the crystals is entirely consistent with the results of solution studies, which also indicate the conformation of the cyclic peptide in the complex to be similar to that of the uncomplexed molecule.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Munksgaard Int PublL Ltd.
Keywords: β turns;calcium binding;crystal structures;cyclic peptide ionophore;membrane transport;molecular conformation
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 25 Feb 2011 09:00
Last Modified: 25 Feb 2011 09:01
URI: http://eprints.iisc.ernet.in/id/eprint/35771

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