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Publication Abstract from PubMed

Crystal structures of native and alpha-D-galactose -bound Bacillus circulans sp. alkalophilusbeta-galactosidase (Bca-beta-gal) were determined at 2.40 A and 2.25 A resolutions, respectively. Bca-beta-gal is a member of family 42 of glycoside hydrolases and it forms a 460 kDa hexameric structure in crystal. The protein consists of three domains in which the catalytic domain has an (alpha/beta)(8) -barrel structure with a cluster of sulfur-rich residues inside the beta-barrel. The shape of the active site is clearly more open compared to the only homological structure available in the Protein Data Bank. This is due to the number of large differences in the loops that connect the C-terminal ends of the beta-strands to N-terminal ends of the alpha-helices within the (alpha/beta)(8) -barrel. The complex structure shows that galactose has bound to the active site as an alpha-anomer and induced clear conformational changes in the active site. The implications of alpha-D-galactose binding to the catalytic mechanism is discussed. In addition, we suggest that beta-galactosidases only utilize mainly reverse hydrolysis mechanism for the synthesis of galacto-oligosaccharides.

Structural analysis, enzymatic characterization, and catalytic mechanisms of beta-galactosidase from Bacillus circulans sp. alkalophilus.,Maksimainen M, Paavilainen S, Hakulinen N, Rouvinen J FEBS J. 2012 Mar 3. doi: 10.1111/j.1742-4658.2012.08555.x. PMID:22385475^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.