Search

Group A carbohydrate (GAC) is a bacterial peptidoglycan-anchored surface rhamnose polysaccharide (RhaPS) that is essential for growth of Streptococcus pyogenes and contributes to its ability to infect the human host. In this study, using molecular and synthetic biology approaches, biochemistry, radiolabeling techniques, and NMR and MS analyses, we examined the role of GacB, encoded in the S. pyogenes GAC gene cluster, in the GAC biosynthesis pathway. We demonstrate that GacB is the first characterized α-d-GlcNAc-β-1,4-l-rhamnosyltransferase that synthesizes the committed step in the biosynthesis of the GAC virulence determinant. Importantly, the substitution of S. pyogenes gacB with the homologous gene from Streptococcus agalactiae (Group B Streptococcus ), Streptococcus equi subsp. zooepidemicus (Group C Streptococcus ), Streptococcus dysgalactiae subsp. equisimilis (Group G Streptococcus ), or Streptococcus mutans complemented the GAC biosynthesis pathway. These results, combined with those from extensive in silico studies, reveal a common phylogenetic origin of the genes required for this priming step in >40 pathogenic species of the Streptococcus genus, including members from the Lancefield Groups B, C, D, E, G, and H. Importantly, this priming step appears to be unique to streptococcal ABC transporter-dependent RhaPS biosynthesis, whereas the Wzx/Wzy-dependent streptococcal capsular polysaccharide pathways instead require an α-d-Glc-β-1,4-l-rhamnosyltransferase. The insights into the RhaPS priming step obtained here open the door to targeting the early steps of the group carbohydrate biosynthesis pathways in species of the Streptococcus genus of high clinical and veterinary importance., Competing Interests: The authors declare that they have no conflicts of interest with the contents of this article., (© 2019 Zorzoli et al.)

Chemical conversion of trisaccharide d-Man beta 1----4-L-Rha alpha 1----3-D-[6-C-3H]Gal into its moraprenyl pyrophosphate derivative is described. Treatment of the latter with the cell envelope preparation from S. anatum results in the formation of polysaccharide with the alpha 1----6 linkage between the trisaccharide units.

Interaction of lithium alcoholates of 2,4-di-O-benzoates of paratose and abequose with tetrabenzyl pyrophosphate gave alpha-phosphates of the 3,6-dideoxyhexoses, further converted into the corresponding cytidine-5'-diphosphate derivatives. These synthetic nucleotides were shown to participate in the biosynthesis of the O-specific polysaccharides for Salmonella typhimurium and S. nitra.

Polyprenyl phosphates of different structure were prepared and their ability to serve as sugar acceptors in the biosynthesis of O-specific polysaccharides of Salmonella anatum was investigated. It was demonstrated that C30-C80-polyprenyl phosphates with unsaturated alpha-isoprene unit were as active as natural acceptor (undecaprenyl phosphate) in this enzymic system. C15- and C100-polyprenyl phosphates of this series were less effective in O-antigen repeating unit formation. Citronellyl and dolichyl phosphates (derivatives of C10- and C105-polyprenols, respectively, with saturated alpha-isoprene unit) were poor substrates. For polymerization of repeating units, the polyprenol chain-length is of utmost importance: its shortening results in a marked drop in the efficiency of respective compounds as substrates.