PplD is a de-N-acetylase of the cell wall linkage unit of streptococcal rhamnopolysaccharides

The cell wall of the bacterial pathogen Group A Streptococcus is decorated with a polysaccharide termed GAC, which is a target for vaccine development. Here, Rush et al. characterize the linkage between GAC and peptidoglycan, and identify a protein that deacetylates the linkage and thus protects the pathogen against host cationic antimicrobial proteins. The cell wall of the human bacterial pathogen Group A Streptococcus (GAS) consists of peptidoglycan decorated with the Lancefield group A carbohydrate (GAC). GAC is a promising target for the development of GAS vaccines. In this study, employing chemical, compositional, and NMR methods, we show that GAC is attached to peptidoglycan via glucosamine 1-phosphate. This structural feature makes the GAC-peptidoglycan linkage highly sensitive to cleavage by nitrous acid and resistant to mild acid conditions. Using this characteristic of the GAS cell wall, we identify PplD as a protein required for deacetylation of linkage N-acetylglucosamine (GlcNAc). X-ray structural analysis indicates that PplD performs catalysis via a modified acid/base mechanism. Genetic surveys in silico together with functional analysis indicate that PplD homologs deacetylate the polysaccharide linkage in many streptococcal species. We further demonstrate that introduction of positive charges to the cell wall by GlcNAc deacetylation protects GAS against host cationic antimicrobial proteins.

Automated summary

The study characterizes the linkage between the polysaccharide GAC and peptidoglycan in the cell wall of Group A Streptococcus, a bacterial pathogen. It identifies a protein, PplD, that deacetylates the linkage and protects the pathogen against host cationic antimicrobial proteins.