The β-galactosidase (BgaC) of the zoonotic pathogen Streptococcus suis is a surface protein without the involvement of bacterial virulence

Abstract

Streptococcal pathogens have evolved to express exoglycosidases, one of which is BgaC β-galactosidase, to deglycosidate host surface glycolconjucates with exposure of the polysaccharide receptor for bacterial adherence. The paradigm BgaC protein is the bgaC product of Streptococcus, a bacterial surface-exposed β-galactosidase. Here we report the functional definition of the BgaC homologue from an epidemic Chinese strain 05ZYH33 of the zoonotic pathogen Streptococcus suis. Bioinformatics analyses revealed that S. suis BgaC shared the conserved active sites (W240, W243 and Y454). The recombinant BgaC protein of S. suis was purified to homogeneity. Enzymatic assays confirmed its activity of β-galactosidase. Also, the hydrolysis activity was found to be region-specific and sugar-specific for the Gal β-1,3-GlcNAc moiety of oligosaccharides. Flow cytometry analyses combined with immune electron microscopy demonstrated that S. suis BgaC is an atypical surface-anchored protein in that it lacks the “LPXTG” motif for typical surface proteins. Integrative evidence from cell lines and mice-based experiments showed that an inactivation of bgaC does not significantly impair the ability of neither adherence nor anti-phagocytosis, and consequently failed to attenuate bacterial virulence, which is somewhat similar to the scenario seen with S. pneumoniae. Therefore we concluded that S. suis BgaC is an atypical surface-exposed protein without the involvement of bacterial virulence.

A unique gene cluster for the utilization of the mucosal and human milk‐associated glycans galacto‐N‐biose and lacto‐N‐biose in Lactobacillus casei

“…GNB-P and LNB-P are hydrolysed to Gal-6P and the corresponding N-acetylhexosamines by the product of the gene gnbG. Only two proteins homologous to GnbG have been characterized to date (Jeong et al, 2009;Hu et al, 2014). The predicted amino acid sequence of GnbG exhibits 60% and 59% identities to the BgaC enzymes from Streptococcus pneumoniae and Streptococcus suis respectively.…”

“…The predicted amino acid sequence of GnbG exhibits 60% and 59% identities to the BgaC enzymes from Streptococcus pneumoniae and Streptococcus suis respectively. These proteins were localized at the bacterial cell surface and they catalysed the hydrolysis of the terminal galactose from lacto-N-tetraose and LNB-containing sugar chains (Jeong et al, 2009;Hu et al, 2014), but not from GNBcontaining sugar chains (Hu et al, 2014). Curiously, like gnbG the bgaC genes from streptococci are also clustered with genes encoding a putative mannose-type PTS (Jeong …”

Two novel regulators of N‐acetyl‐galactosamine utilization pathway and distinct roles in bacterial infections

“…2012; Hu et al. 2014). Bacterial adherence was tested with Hep‐2 cell line, and the evaluation for ability of anti‐phagocytosis was based on the Raw264.7 cells.…”

Isolation and characterization of a native avirulent strain of Streptococcus suis serotype 2: a perspective for vaccine development

“…As described by Hu et al. 38 , cells were infected with labeled bacteria (ratio 1:100) and then incubated at 37°C for 2 h with gentle agitation. Following incubation, 4% (w/v) paraformaldehyde in PBS was added to each tube to fix cells.…”