title: The Extracellular Wall-Bound β-N-Acetylglucosaminidase from Lactobacillus casei Is Involved in the Metabolism of the Human Milk Oligosaccharide Lacto-N-Triose.
abstract: Human milk oligosaccharides (HMOs) are considered to play a key role in establishing and maintaining the infant gut microbiota. Lacto-N-triose forms part of both type 1 and type 2 HMOs and also of the glycan moieties of glycoproteins. Upstream of the previously characterized gene cluster involved in lacto-N-biose and galacto-N-biose metabolism from Lactobacillus casei BL23, there are two genes, bnaG and manA, encoding a β-N-acetylglucosaminidase precursor and a mannose-6-phosphate isomerase, respectively. In this work, we show that L. casei is able to grow in the presence of lacto-N-triose as a carbon source. Inactivation of bnaG abolished the growth of L. casei on this oligosaccharide, demonstrating that BnaG is involved in its metabolism. Interestingly, whole cells of a bnaG mutant were totally devoid of β-N-acetylglucosaminidase activity, suggesting that BnaG is an extracellular wall-attached enzyme. In addition to hydrolyzing lacto-N-triose into N-acetylglucosamine and lactose, the purified BnaG enzyme also catalyzed the hydrolysis of 3'-N-acetylglucosaminyl-mannose and 3'-N-acetylgalactosaminyl-galactose. L. casei can be cultured in the presence of 3'-N-acetylglucosaminyl-mannose as a carbon source, but, curiously, the bnaG mutant strain was not impaired in its utilization. These results indicate that the assimilation of 3'-N-acetylglucosaminyl-mannose is independent of BnaG. Enzyme activity and growth analysis with a manA-knockout mutant showed that ManA is involved in the utilization of the mannose moiety of 3'-N-acetylglucosaminyl-mannose. Here we describe the physiological role of a β-N-acetylglucosaminidase in lactobacilli, and it supports the metabolic adaptation of L. casei to the N-acetylglucosaminide-rich gut niche.
authors.affiliation: Laboratorio de Bacterias Lácticas y Probióticos, Departamento de Biotecnología de Alimentos, IATA-CSIC, Valencia, Spain.
authors.forename: Gonzalo N
authors.initials: GN
authors.lastname: Bidart
authors.affiliation: Laboratorio de Bacterias Lácticas y Probióticos, Departamento de Biotecnología de Alimentos, IATA-CSIC, Valencia, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Rodríguez-Díaz
authors.affiliation: Laboratorio de Bacterias Lácticas y Probióticos, Departamento de Biotecnología de Alimentos, IATA-CSIC, Valencia, Spain yebra@iata.csic.es.
authors.forename: María J
authors.initials: MJ
authors.lastname: Yebra
mesh_terms: D000118:Acetylglucosaminidase / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D007780:Lacticaseibacillus casei / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008895:Milk, Human / Q000378:metabolism / Q000382:microbiology*; D009844:Oligosaccharides / Q000378:metabolism; D014312:Trisaccharides / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D009844:Oligosaccharides; D014312:Trisaccharides; C014636:lacto-N-triose I; D000118:Acetylglucosaminidase