InterPro domain: IPR001119

S-layers are paracrystalline mono-layered assemblies of (glyco)proteins which coat the surface of bacteria [ 1 , 2 ]. Several S-layer proteins and some other cell wall proteins contain one or more copies of a domain of about 50-60 residues, which has been called SLH (for S-layer homology). Although it was originally proposed that SLH domains bind to peptidoglycan, it is now evident that pyruvylated secondary cell wall polymers (SCWPs), which are either teichoic acids, teichuronic acids, lipoteichoic acids or lipoglycans, serve as the anchoring structures for SLH motifs in the Gram-positive cell wall [ 3 , 4 ]. However, the study of S-layer protein SbpA of Bacillus sphaericus revealed that SLH motifs are not sufficient for specific binding to SCWPs. Thus, the molecular basis explaining SLH affinity and specificity of interaction with cell wall polymers are not completely elucidated [ 5 ].

1. Bacterial S-layers. Trends Microbiol. 7, 253-60
2. S-Layer proteins. J. Bacteriol. 182, 859-68
3. Structural research on surface layers: a focus on stability, surface layer homology domains, and surface layer-cell wall interactions. J. Struct. Biol. 124, 276-302
4. The structure of secondary cell wall polymers: how Gram-positive bacteria stick their cell walls together. Microbiology (Reading, Engl.) 151, 643-51
5. Protein cell surface display in Gram-positive bacteria: from single protein to macromolecular protein structure. FEMS Microbiol. Lett. 256, 1-15