1gca
From Proteopedia
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THE 1.7 ANGSTROMS REFINED X-RAY STRUCTURE OF THE PERIPLASMIC GLUCOSE(SLASH)GALACTOSE RECEPTOR FROM SALMONELLA TYPHIMURIUM
Overview
The X-ray structure of the periplasmic glucose/galactose receptor (binding, protein) of Salmonella typhimurium (GBP-S) has been refined at 1.7 A, resolution with an R-factor of 19.0%. The model contains all 309 residues, of the amino acid sequence, 153 water molecules, a calcium ion and, beta-D-galactose. The protein consists of two very similar structural, domains, each of which is composed a core of parallel beta-sheet flanked, on both sides by alpha-helices. Three short stretches of amino acid chain, (from symmetrically related portions of the structure) link the domains, and presumably act as a hinge to allow their relative movement in, functionally important conformational changes. Galactose is bound between, the domains, interacting with a number of side-chains from the loops, lining the binding cleft. A combination of hydrogen bonding, hydrophobic, and steric effects give rise to tight binding (dissociation constant 0.2, microM) and high specificity. Of nine hydrogen bonding groups, three are, aspartate, three asparagine, one histidine (unprotonated), one arginine, and one water, contributing 13 hydrogen bonds in total. Additional, residues pack against (primarily) non-polar faces of the sugar molecule., The precise arrangement of the hydrogen bonding and hydrophobic residues, results in an enclosed binding site with a shape that is a composite of, those of the allowed sugar molecules. It is presumed that ligands bind to, a more open form of the receptor that then closes by rotation in the, hinge. Comparison with the GBP-S structure solved earlier in complex with, glucose shows no significant changes, even for the aspartate residue most, directly involved with the different sugars. Comparison with the, galactose/glucose receptor of Escherichia coli indicates that these two, proteins are very similar in overall structure, with the main difference, being a 2 to 3 degrees rotation in the hinge. This difference appears to, be the result of different crystal packing for the two proteins; it is, likely that both conformations are normally found in solution.
About this Structure
1GCA is a Single protein structure of sequence from Salmonella typhimurium with GAL and CA as ligands. Full crystallographic information is available from OCA.
Reference
The 1.7 A refined X-ray structure of the periplasmic glucose/galactose receptor from Salmonella typhimurium., Zou JY, Flocco MM, Mowbray SL, J Mol Biol. 1993 Oct 20;233(4):739-52. PMID:8240551
Page seeded by OCA on Tue Nov 20 15:56:00 2007
