8Q51

Beta-galactosidase from Bacillus circulans conformational state 2

Summary for 8Q51

• Entry DOI: 10.2210/pdb8q51/pdb
• EMDB information: 18157
• Descriptor: beta-galactosidase (1 entity in total)
• Functional Keywords: galactosidase, transgalactosylation, izoform a, enzyme, hydrolase
• Biological source: Niallia circulans
• Total number of polymer chains: 1
• Total formula weight: 192584.39

Authors

Kascakova, B.,Hovorkova, M.,Petraskova, L.,Novacek, J.,Pinkas, D.,Gardian, Z.,Kren, V.,Bojarova, P.,Kuta Smatanova, I. (deposition date: 2023-08-07, release date: 2024-10-16, Last modification date: 2024-11-20)

Primary citation

Hovorkova, M.,Kascakova, B.,Petraskova, L.,Havlickova, P.,Novacek, J.,Pinkas, D.,Gardian, Z.,Kren, V.,Bojarova, P.,Smatanova, I.K.
The variable structural flexibility of the Bacillus circulans beta-galactosidase isoforms determines their unique functionalities.
Structure, 32:2023-2037.e5, 2024

PubMed Abstract: β-Galactosidase from Bacillus circulans ATCC 31382 (BgaD) is a biotechnologically important enzyme for the synthesis of β-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 β-galactosidase catalysis, with implications for tailored GOS production.

PubMed: 39353423
DOI: 10.1016/j.str.2024.09.005

Experimental method

ELECTRON MICROSCOPY (4 Å)