title: Distinct roles of β-galactosidase paralogues of the rumen bacterium Mannheimia succiniciproducens.
abstract: Mannheimia succiniciproducens, a rumen bacterium belonging to the family Pasteurellaceae, has two putative β-galactosidase genes, bgaA and bgaB, encoding polypeptides whose deduced amino acid sequences share 56% identity with each other and show approximately 30% identity to the Escherichia coli gene for LacZ. The M. succiniciproducens bgaA (MsbgaA) gene-deletion mutant was not able to grow on lactose as the sole carbon source, suggesting its essential role in lactose metabolism, whereas the MsbgaB gene-deletion mutant did not show any growth defect on a lactose medium. Furthermore, the expression of the MsbgaA gene was induced by the addition of lactose in the growth medium, whereas the MsbgaB gene was constitutively expressed independently of a carbon source. Biochemical characterization of the recombinant proteins revealed that MsBgaA is more efficient than MsBgaB in hydrolyzing o-nitrophenyl-β-d-galactopyranoside and p-nitrophenyl-β-d-galactopyranoside. MsBgaA was highly specific for the hydrolysis of lactose, with a catalytic efficiency of 46.9 s(-1) mM(-1). However, MsBgaB was more efficient for the hydrolysis of lactulose than lactose, and the catalytic efficiency was 10.0 s(-1) mM(-1). Taken together, our results suggest that the β-galactosidase paralogues of M. succiniciproducens BgaA and BgaB play a critical role in lactose metabolism and in an unknown but likely specific function for rumen bacteria, respectively.
authors.affiliation: Integrative Omics Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea.
authors.forename: Eun-Gyeong
authors.initials: EG
authors.lastname: Lee
authors.forename: Seonghun
authors.initials: S
authors.lastname: Kim
authors.forename: Doo-Byoung
authors.initials: DB
authors.lastname: Oh
authors.forename: Sang Yup
authors.initials: SY
authors.lastname: Lee
authors.forename: Ohsuk
authors.initials: O
authors.lastname: Kwon
mesh_terms: D000818:Animals; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D006863:Hydrogen-Ion Concentration; D007785:Lactose; D031121:Mannheimia / Q000201:enzymology*; D010802:Phylogeny; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012417:Rumen / Q000382:microbiology*; D012418:Ruminants; D013379:Substrate Specificity; D013696:Temperature; D001616:beta-Galactosidase / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D001616:beta-Galactosidase; D007785:Lactose
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