Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
Glycobiology. 2013 Feb;23(2):232-40. doi: 10.1093/glycob/cws142. Epub 2012 Oct 22.
Bifidobacterium bifidum is one of the most frequently found bifidobacteria in the intestines of newborn infants. We previously reported that B. bifidum possesses unique metabolic pathways for O-linked glycans on gastrointestinal mucin (Yoshida E, Sakurama H, Kiyohara M, Nakajima M, Kitaoka M, Ashida H, Hirose J, Katayama T, Yamamoto K, Kumagai H. 2012. Bifidobacterium longum subsp. infantis uses two different β-galactosidases for selectively degrading type-1 and type-2 human milk oligosaccharides. Glycobiology. 22:361-368). The nonreducing termini of O-linked glycans on mucin are frequently covered with histo-blood group antigens. Here, we identified a gene agabb from B. bifidum JCM 1254, which encodes glycoside hydrolase (GH) family 110 α-galactosidase. AgaBb is a 1289-amino acid polypeptide containing an N-terminal signal sequence, a GH110 domain, a carbohydrate-binding module (CBM) 51 domain, a bacterial Ig-like (Big) 2 domain and a C-terminal transmembrane region, in this order. The recombinant enzyme expressed in Escherichia coli hydrolyzed α1,3-linked Gal in branched blood group B antigen [Galα1-3(Fucα1-2)Galβ1-R], but not in a linear xenotransplantation antigen (Galα1-3Galβ1-R). The enzyme also acted on group B human salivary mucin and erythrocytes. We also revealed that CBM51 specifically bound blood group B antigen using both isothermal titration calorimetry and a solid-phase binding assay, and it enhanced the affinity of the enzyme toward substrates with multivalent B antigens. We suggest that this enzyme plays an important role in degrading B antigens to acquire nutrients from mucin oligosaccharides in the gastrointestinal tracts.
两歧双歧杆菌是新生婴儿肠道中最常发现的双歧杆菌之一。我们之前报道过，两歧双歧杆菌具有独特的胃肠道粘蛋白 O-连接聚糖的代谢途径（Yoshida E、Sakurama H、Kiyohara M、Nakajima M、Kitaoka M、Ashida H、Hirose J、Katayama T、Yamamoto K、Kumagai H. 2012. 长双歧杆菌亚种。婴儿使用两种不同的β-半乳糖苷酶选择性降解 1 型和 2 型人乳寡糖。糖生物学。22:361-368）。粘蛋白上 O-连接聚糖的非还原末端经常被组织血型抗原覆盖。在这里，我们从两歧双歧杆菌 JCM 1254 中鉴定出一个基因 agabb，它编码糖苷水解酶（GH）家族 110 α-半乳糖苷酶。AgaBb 是一个 1289 个氨基酸的多肽，包含一个 N 端信号序列、一个 GH110 结构域、一个碳水化合物结合模块（CBM）51 结构域、一个细菌免疫球蛋白样（Big）2 结构域和一个 C 端跨膜区，顺序排列。在大肠杆菌中表达的重组酶水解了支链血型 B 抗原[Galα1-3（Fucα1-2）Galβ1-R]中的α1,3-连接的 Gal，但不能水解线性异种移植抗原（Galα1-3Galβ1-R）。该酶还作用于 B 型人唾液粘蛋白和红细胞。我们还揭示了 CBM51 特异性结合血型 B 抗原，使用等温滴定量热法和固相结合测定法，并增强了酶对具有多价 B 抗原的底物的亲和力。我们认为，这种酶在从胃肠道粘蛋白寡糖中获取营养物质方面发挥了重要作用，降解 B 抗原。
