2liv
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(New page: 200px<br /><applet load="2liv" size="450" color="white" frame="true" align="right" spinBox="true" caption="2liv, resolution 2.4Å" /> '''PERIPLASMIC BINDING P...)
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Revision as of 10:35, 21 November 2007
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PERIPLASMIC BINDING PROTEIN STRUCTURE AND FUNCTION. REFINED X-RAY STRUCTURES OF THE LEUCINE/ISOLEUCINE/VALINE-BINDING PROTEIN AND ITS COMPLEX WITH LEUCINE
Overview
The three-dimensional structure of the native unliganded form of the, Leu/Ile/Val-binding protein (Mr = 36,700), an essential component of the, high-affinity active transport system for the branched aliphatic amino, acids in Escherichia coli, has been determined and further refined to a, crystallographic R-factor of 0.17 at 2.4 A resolution. The entire, structure consists of 2710 non-hydrogen atoms from the complete sequence, of 344 residues and 121 ordered water molecules. Bond lengths and angle, distances in the refined model have root-mean-square deviations from ideal, values of 0.05 A and 0.10 A, respectively. The overall shape of the, protein is a prolate ellipsoid with dimensions of 35 A x 40 A x 70 A. The, protein consists of two distinct globular domains linked by three short, peptide segments which, though widely separated in the sequence, are, proximal in the tertiary structure and form the base of the deep cleft, between the two domains. Although each domain is built from polypeptide, segments located in both the amino (N) and the carboxy (C) terminal, halves, both domains exhibit very similar supersecondary structures, consisting of a central beta-sheet of seven strands flanked on either side, by two or three helices. The two domains are far apart from each other, leaving the cleft wide open by about 18 A. The cleft has a depth of about, 15 A and a base of about 14 A x 16 A. Refining independently the structure, of native Leu/Ile/Val-binding protein crystals soaked in a solution, containing L-leucine at 2.8 A resolution (R-factor = 0.15), we have been, able to locate and characterize an initial, major portion of the, substrate-binding site of the Leu/Ile/Val-binding protein. The binding of, the L-leucine substrate does not alter the native crystal structure, and, the L-leucine is lodged in a crevice on the wall of the N-domain, which is, in the inter-domain cleft. The L-leucine is held in place primarily by, hydrogen-bonding of its alpha-ammonium and alpha-carboxylate groups with, main-chain peptide units and hydroxyl side-chain groups; there are no, salt-linkages. The charges on the leucine zwitterion are stabilized by, hydrogen-bond dipoles. The side-chain of the L-leucine substrate lies in a, depression lined with non-polar residues, including Leu77, which confers, specificity to the site by stacking with the side-chain of the leucine, substrate.(ABSTRACT TRUNCATED AT 400 WORDS)
About this Structure
2LIV is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Periplasmic binding protein structure and function. Refined X-ray structures of the leucine/isoleucine/valine-binding protein and its complex with leucine., Sack JS, Saper MA, Quiocho FA, J Mol Biol. 1989 Mar 5;206(1):171-91. PMID:2649682
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