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spinqualitylabelsall models 1kwk, resolution 2.20Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal structure of Thermus thermophilus A4 beta-galactosidase in complex with galactose

Overview

The beta-galactosidase from an extreme thermophile, Thermus thermophilus, A4 (A4-beta-Gal), is thermostable and belongs to the glycoside hydrolase, family 42 (GH-42). As the first known structures of a GH-42 enzyme, we, determined the crystal structures of free and galactose-bound A4-beta-Gal, at 1.6A and 2.2A resolution, respectively. A4-beta-Gal forms a, homotrimeric structure resembling a flowerpot. Each monomer has an active, site located inside a large central tunnel. The N-terminal domain of, A4-beta-Gal has a TIM barrel fold, as predicted from hydrophobic cluster, analysis. The putative catalytic residues of A4-beta-Gal (Glu141 and, Glu312) superimpose well with the catalytic residues of Escherichia coli, beta-galactosidase. The environment around the catalytic nucleophile, (Glu312) is similar to that in the case of E.coli beta-galactosidase, but, the recognition mechanism for a substrate is different. Trp182 of the next, subunit of the trimer constitutes a part of the active-site pocket, indicating that the trimeric structure is essential for the enzyme, activity. Structural comparison with other glycoside hydrolases revealed, that many features of the 4/7 superfamily are conserved in the A4-beta-Gal, structure. On the basis of the results of 1H NMR spectroscopy, A4-beta-Gal, was determined to be a "retaining" enzyme. Interestingly, the active site, was similar with those of retaining enzymes, but the overall fold of the, TIM barrel domain was very similar to that of an inverting enzyme, beta-amylase.

About this Structure

1KWK is a Single protein structure of sequence from Thermus thermophilus with GAL, CL, ACT, ZN and MPD as ligands. Active as Beta-galactosidase, with EC number 3.2.1.23 Full crystallographic information is available from OCA.

Reference

Trimeric crystal structure of the glycoside hydrolase family 42 beta-galactosidase from Thermus thermophilus A4 and the structure of its complex with galactose., Hidaka M, Fushinobu S, Ohtsu N, Motoshima H, Matsuzawa H, Shoun H, Wakagi T, J Mol Biol. 2002 Sep 6;322(1):79-91. PMID:12215416

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