Bacterial SLH domain proteins are non-covalently anchored to the cell surface via a conserved mechanism involving wall polysaccharide pyruvylation

Several bacterial proteins are non-covalently anchored to the cell surface via an S-layer homology (SLH) domain. Previous studies have suggested that this cell surface display mechanism involves a noncovalent interaction betw een the SLH domain and peptidoglycan-associated polymers. Here we report th e characterization of a two-gene operon, csaAB, for cell surface anchoring, in Bacillus anthracis, Its distal open reading frame (csaB) is required fo r the retention of SLH-containing proteins on the cell wall. Biochemical an alysis of cell wall components showed that CsaB was involved in the additio n of a pyruvyl group to a peptidoglycan-associated polysaccharide fraction, and that this modification was necessary for binding of the SLH domain. Th e csaAB operon is present in several bacterial species that synthesize SLH- containing proteins. This observation and the presence of pyruvate in the c ell wall of the corresponding bacteria suggest that the mechanism described in this study is widespread among bacteria.