1c7t

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spinqualitylabelsall models 1c7t, resolution 1.90Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

BETA-N-ACETYLHEXOSAMINIDASE MUTANT E540D COMPLEXED WITH DI-N ACETYL-D-GLUCOSAMINE (CHITOBIASE)

Overview

The catalytic domain of chitobiase (beta-N-1-4 acetylhexosaminidase) from, Serratia marcescens, is an alpha/beta TIM-barrel. This enzyme belongs to, family 20 of glycosyl hydrolases in which a conserved amino acid pair, aspartate-glutamate, is present (Asp539-Glu540). It was proposed that, catalysis by this enzyme family is carried out by glutamate 540 acting as, a proton donor and by the acetamido group of the substrate as a, nucleophile. We investigated the role of Asp539 and Glu540 by, site-directed mutagenesis, biochemical characterization and by structural, analyses of chitobiase -substrate co-crystals. We found that both residues, are essential for chitobiase activity. The mutations, however, led to, subtle changes in the catalytic site. Our results support the model that, Glu540 acts as the proton donor and that Asp539 acts in several different, ways. Asp539 restrains the acetamido group of the substrate in a specific, orientation by forming a hydrogen bond with N2 of the non-reduced (-1), sugar. In addition, this residue participates in substrate binding. It is, also required for the correct positioning of Glu540 and may provide, additional negative charge at the active site. Thus, these biochemical and, structural studies provide a molecular explanation for the functional, importance and conservation of these residues.

About this Structure

1C7T is a Single protein structure of sequence from Serratia marcescens with CBS and SO4 as ligands. Active as Beta-N-acetylhexosaminidase, with EC number 3.2.1.52 Full crystallographic information is available from OCA.

Reference

Structures of chitobiase mutants complexed with the substrate Di-N-acetyl-d-glucosamine: the catalytic role of the conserved acidic pair, aspartate 539 and glutamate 540., Prag G, Papanikolau Y, Tavlas G, Vorgias CE, Petratos K, Oppenheim AB, J Mol Biol. 2000 Jul 14;300(3):611-7. PMID:10884356

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