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Publication Abstract from PubMed

beta-Galactosidase from Bacillus circulans ATCC 31382 (BgaD) is a biotechnologically important enzyme for the synthesis of beta-galactooligosaccharides (GOS). Among its four isoforms, isoform A (BgaD-A) has distinct synthetic properties. Here, we present cryoelectron microscopy (cryo-EM) structures of BgaD-A and compare them with the known X-ray crystal structure of isoform D (BgaD-D), revealing substantial structural divergences between the two isoforms. In contrast to BgaD-D, BgaD-A features a flexible Big-4 domain and another enigmatic domain. The newly identified flexible region in BgaD-A is termed as "barrier domain 8," and serves as a barricade, obstructing the access of longer oligosaccharide substrates into the active site of BgaD-A. The transgalactosylation reactions catalyzed by both isoforms revealed that BgaD-A has a higher selectivity than BgaD-D in the earlier stages of the reaction and is prevailingly directed to shorter galactooligosaccharides. This study improves our understanding of the structural determinants governing beta-galactosidase catalysis, with implications for tailored GOS production.

The variable structural flexibility of the Bacillus circulans beta-galactosidase isoforms determines their unique functionalities.,Hovorkova M, Kascakova B, Petraskova L, Havlickova P, Novacek J, Pinkas D, Gardian Z, Kren V, Bojarova P, Smatanova IK Structure. 2024 Sep 26:S0969-2126(24)00374-5. doi: 10.1016/j.str.2024.09.005. PMID:39353423^[1]

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