1swt

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spinqualitylabelsall models 1swt, resolution 2.00Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CORE-STREPTAVIDIN MUTANT D128A IN COMPLEX WITH BIOTIN AT PH 4.5

Overview

It is currently unclear whether small molecules dissociate from a protein, binding site along a defined pathway or through a collection of, dissociation pathways. We report herein a joint crystallographic, computational, and biophysical study that suggests the Asp-128 --> Ala, (D128A) streptavidin mutant closely mimics an intermediate on a, well-defined dissociation pathway. Asp-128 is hydrogen bonded to a ureido, nitrogen of biotin and also networks with the important aromatic binding, contacts Trp-92 and Trp-108. The Asn-23 hydrogen bond to the ureido oxygen, of biotin is lengthened to 3.8 A in the D128A structure, and a water, molecule has moved into the pocket to replace the missing carboxylate, interaction. These alterations are accompanied by the coupled movement of, biotin, the flexible binding loop containing Ser-45, and the loop, containing the Ser-27 hydrogen bonding contact. This structure closely, parallels a key intermediate observed in a potential of mean, force-simulated dissociation pathway of native streptavidin, where the, Asn-23 hydrogen bond breaks first, accompanied by the replacement of the, Asp-128 hydrogen bond by an entering water molecule. Furthermore, both, biotin and the flexible loop move in a concerted conformational change, that closely approximates the D128A structural changes. The activation and, thermodynamic parameters for the D128A mutant were measured and are, consistent with an intermediate that has traversed the early portion of, the dissociation reaction coordinate through endothermic bond breaking and, concomitant gain in configurational entropy. These composite results, suggest that the D128A mutant provides a structural "snapshot" of an early, intermediate on a relatively well-defined dissociation pathway for biotin.

About this Structure

1SWT is a Single protein structure of sequence from Streptomyces avidinii with BTN as ligand. Full crystallographic information is available from OCA.

Reference

A structural snapshot of an intermediate on the streptavidin-biotin dissociation pathway., Freitag S, Chu V, Penzotti JE, Klumb LA, To R, Hyre D, Le Trong I, Lybrand TP, Stenkamp RE, Stayton PS, Proc Natl Acad Sci U S A. 1999 Jul 20;96(15):8384-9. PMID:10411884

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