Assembly and Function of the Bacillus anthracis S-Layer

Abstract

Bacillus anthracis, the anthrax agent, is a member of the Bacillus cereus sensu lato group, which includes invasive pathogens of mammals or insects as well as nonpathogenic environmental strains. The genes for anthrax pathogenesis are located on two large virulence plasmids. Similar virulence plasmids have been acquired by other B. cereus strains and enable the pathogenesis of anthrax-like diseases. Among the virulence factors of B. anthracis is the S-layer-associated protein BslA, which endows bacilli with invasive attributes for mammalian hosts. BslA surface display and function are dependent on the bacterial S-layer, whose constituents assemble by binding to the secondary cell wall polysaccharide (SCWP) via S-layer homology (SLH) domains. B. anthracis and other pathogenic B. cereus isolates harbor genes for the secretion of S-layer proteins, for S-layer assembly, and for synthesis of the SCWP. We review here recent insights into the assembly and function of the S-layer and the SCWP.

Functional Characterization of Enzymatic Steps Involved in Pyruvylation of Bacterial Secondary Cell Wall Polymer Fragments

“…These findings let us conclude that either a longer SCWP building block, or a lipid-linked precursor was needed. Since more likely from a biosynthetic perspective and supported by the current model of SCWP biosynthesis in B. anthracis , where non-stoichiometric modifications of the repeats would occur at the lipid-linked stage ( Missiakas and Schneewind, 2017 ), we decided for the latter option and set up a stepwise enzymatic cascade to reach our target molecule.…”

“…Generally, polymerization of SCWP repeats and SCWP ligation to peptidoglycan are remaining challenging open questions in SCWP biosynthesis pathways. According to a recent model of B. anthracis SCWP biosynthesis ( Missiakas and Schneewind, 2017 ; Oh et al, 2017 ), an undecaprenyl-pyrophosphate linked GlcNAc-GlcNAc-ManNAc trisaccharide repeat would be preassembled in a cytoplasmic, TagO and TagA1/-2 catalyzed reaction followed by membrane flipping involving the multidrug and toxin extrusion-like protein Bas5279. At the outer surface of the cytoplasmic membrane, the lipid-bound SCWP would be ligated onto murein linkage units and the final polymer would be attached to peptidoglycan by a LytR-CpsA-Psr ligase.…”

Galactosylation of the Secondary Cell Wall Polysaccharide of Bacillus anthracis and Its Contribution to Anthrax Pathogenesis

“…In contrast, galE1 is only expressed during vegetative growth and provides UDP-Gal for the galactosylation of the SCWP in B. anthracis. Unlike genes located within the sps locus, galE1 is conserved among all members of the B. cereus sensu lato group whose SCWPs contain galactosyl modifications (18). The lcpC gene, which is located immediately adjacent to galE1 within the sps locus, is conserved in a manner similar to galE1.…”

“…We sought to identify the genetic basis for SCWP galactosylation, which is likely dependent on UDP-galactose (UDP-Gal) as the substrate for glucosyltransferases that modify the presumed cytoplasmic precursor of wall polysaccharide synthesis, the undecaprenyl-pyrophosphate-linked trisaccharide C 55 -(PO 4 ) 2 -ManNAc-(1¡4)-␤-GlcNAc-(1¡6)-␣-GlcNAc] (18). Earlier work characterized three gene products of B. anthracis that had been annotated as UDP-glucose 4-epimerase: BAS1093, galE1 (BAS5114), and galE2 (BAS5304) (19).…”

Comparing proteins and nucleic acids for next-generation biomolecular engineering

“…Sheet-like assemblies are found in bacterial S-layers ( Figure 4A), that function as sole structural exoskeleton for almost all archaea and in eubacteria as attachment matrix for exoenzymes or to invade host cells, such as for Bacillus anthracis layers [141][142][143] . The SbsB protein lattice from a Gram-positive bacterium illustrates this molecular architecture ( Figure 4A) 144 Figure 4C) and facilitate the clathrin-independent formation of vesicle pits 152 .…”