1gub

From Proteopedia

Revision as of 13:27, 18 December 2007

HINGE-BENDING MOTION OF D-ALLOSE BINDING PROTEIN FROM ESCHERICHIA COLI: THREE OPEN CONFORMATIONS

Overview

ABC transport systems for import or export of nutrients and other, substances across the cell membrane are widely distributed in nature. In, most bacterial systems, a periplasmic component is the primary determinant, of specificity of the transport complex as a whole. We report here the, crystal structure of the periplasmic binding protein for the allose system, (ALBP) from Escherichia coli, solved at 1.8 A resolution using the, molecular replacement method. As in the other members of the family, (especially the ribose binding protein, RBP, with which it shares 35 %, sequence homology), this structure consists of two similar domains joined, by a three-stranded hinge region. The protein is believed to exist in a, dynamic equilibrium of closed and open conformations in solution which is, an important part of its function. In the closed ligand-bound form, observed here, D-allose is buried at the domain interface. Only the, beta-anomer of allopyranose is seen in the crystal structure, although the, alpha-anomer can potentially bind with a similar affinity. Details of the, ligand-binding cleft reveal the features that determine substrate, specificity. Extensive hydrogen bonding as well as hydrophobic, interactions are found to be important. Altogether ten residues from both, the domains form 14 hydrogen bonds with the sugar. In addition, three, aromatic rings, one from each domain with faces parallel to the plane of, the sugar ring and a third perpendicular, make up a hydrophobic stacking, surface for the ring hydrogen atoms. Our results indicate that the, aromatic rings forming the sugar binding cleft can sterically block the, binding of any hexose epimer except D-allose, 6-deoxy-allose or, 3-deoxy-glucose; the latter two are expected to bind with reduced, affinity, due to the loss of some hydrogen bonds. The pyranose form of the, pentose, D-ribose, can also fit into the ALBP binding cleft, although with, lower binding affinity. Thus, ALBP can function as a low affinity, transporter for D-ribose. The significance of these results is discussed, in the context of the function of allose and ribose transport systems.

About this Structure

1GUB is a Single protein structure of sequence from Escherichia coli with NI as ligand. Known structural/functional Site: . Full crystallographic information is available from OCA.

Reference

Structure of D-allose binding protein from Escherichia coli bound to D-allose at 1.8 A resolution., Chaudhuri BN, Ko J, Park C, Jones TA, Mowbray SL, J Mol Biol. 1999 Mar 12;286(5):1519-31. PMID:10064713

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