1i93

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NMR ENSEMBLE OF ION-SELECTIVE LIGAND D16 FOR PLATELET INTEGRIN ALPHAIIB-BETA3

Overview

Integrins contain a number of divalent cation binding sites that control, ligand binding affinity. Ions such as Ca(2+) and Mg(2+) bind to distinct, sites on integrin and can have opposing effects on ligand binding. These, effects are presumably brought about by alterations of the shape of the, ligand binding pocket. To gain insight into the nature of these structural, differences, we probed the integrin ligand binding site with an RGD-based, library of unparalleled complexity. A cysteine-constrained phage library, containing six random amino acids and the RGD motif present in seven, different registers was used to select for ligands that exhibit, ion-selective binding to integrin alpha(IIb)beta(3). The library was used, to select for peptides that bind to the integrin alpha(IIb)beta(3), preferentially in Ca(2+) versus Mg(2+). Peptides were identified which, bound selectively in each ion. The Ca(2+)-selective peptides had a range, of sequences, with the only obvious consensus involving a motif that had, four cysteine residues bonded in a 1,4:2,3 arrangement. Interestingly, though, the Mg(2+)-selective peptides exhibited a well defined consensus, motif containing Cys-X-aromatic-L/G-R-G-D-hydrophobic-R-R/K-Cys. As a, first step toward understanding the structural basis for this selectivity, solution NMR structures were obtained for representatives of both sets of, peptides. All peptides formed turns, with the RGD motif at the apex. The, Mg(2+)-selected peptides contained a unique basic patch that protrudes, from the base of the turn.

About this Structure

1I93 is a Protein complex structure of sequences from [1] with ACE and NH2 as ligands. Full crystallographic information is available from OCA.

Reference

Selection and structure of ion-selective ligands for platelet integrin alpha IIb(beta) 3., Smith JW, Le Calvez H, Parra-Gessert L, Preece NE, Jia X, Assa-Munt N, J Biol Chem. 2002 Mar 22;277(12):10298-305. Epub 2001 Dec 17. PMID:11748219

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