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

Abstract

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 between the SLH domain and peptidoglycan-associated polymers. Here we report the characterization of a two-gene operon, csaAB, for cell surface anchoring, in Bacillus anthracis. Its distal open reading frame (csaB) is required for the retention of SLH-containing proteins on the cell wall. Biochemical analysis of cell wall components showed that CsaB was involved in the addition of a pyruvyl group to a peptidoglycan-associated polysaccharide fraction, and that this modi®cation was necessary for binding of the SLH domain. The csaAB operon is present in several bacterial species that synthesize SLHcontaining proteins. This observation and the presence of pyruvate in the cell wall of the corresponding bacteria suggest that the mechanism described in this study is widespread among bacteria.

The structure of secondary cell wall polymers: how Gram-positive bacteria stick their cell walls together

“…The high metabolic load associated with the biosynthesis of S-layer proteins, together with their prominent cellular location, indicates that they provide a positive selective advantage in the environment. It is conceivable that the stable attachment of S-layer (glyco)-proteins to the cell wall is important for the cell, and 'nonclassical' SCWPs have been identified as mediators for non-covalent attachment of S-layers to the underlying PG meshwork (Cava et al, 2004;Mesnage et al, 2000;Sára, 2001) (Fig. 1).…”

“…Pyruvic-acid-containing SCWPs have also been reported for the S-layer carrying organisms Bacillus sphaericus CCM 2177 (Ilk et al, 1999) and Bacillus anthracis (Mesnage et al, 2000); however, information is not available on either their full structures or their linkage to the PG layer.…”

“…Recently, the cell-wall-targeting mechanism of S-layer proteins has been investigated in more detail (Cava et al, 2004;Mesnage et al, 2000;Sára, 2001). These studies suggest that, in general, S-layer proteins have two functional regions: a cell-wall-targeting domain, which in most of the organisms investigated thus far is located at the N-terminus, and a C-terminal self-assembly domain.…”

“…the cellulosomes (Bayer et al, 2004) or other surface-associated enzymes (Liu et al, 1996). In the case of Bacillus anthracis, the aetiological agent of anthrax, the molecular basis of the interaction between SLH domains and SCWPs was established by elucidating their binding properties (Mesnage et al, 2000). Both S-layer proteins of B. anthracis (EA1 and Sap) possess SLH domains that bind the S-layer proteins directly to PG (Mesnage et al, 1997(Mesnage et al, , 1999.…”

Bacillus anthracis SlaQ Promotes S-Layer Protein Assembly

“…B. anthracis variants lacking the S-layer protein Sap cannot restrict BslO localization to septal rings; similar to bslO mutants, sap variants form elongated chains of vegetative bacilli (16). csaB mutants display the most severe cell separation defect, and the variants are unable to deposit any S-layer or S-layer-associated proteins with SLH domains in the envelope of B. anthracis (17,21). csaB is thought to encode a pyruvyl transferase that transfers ketal-pyruvyl onto the terminal ␤-ManNAc residue at the distal end of the SCWP (20).…”