biostudies-literatureKern JNIAID NIH HHSNIGMS NIH HHS26042-9https://www.ebi.ac.uk/biostudies/studies/S-EPMC3138252biostudies-literatureUnknown286(29)Surface (S)-layers, para-crystalline arrays of protein, are deposited in the envelope of most bacterial species. These surface organelles are retained in the bacterial envelope through the non-covalent association of proteins with cell wall carbohydrates. Bacillus anthracis, a Gram-positive pathogen, produces S-layers of the protein Sap, which uses three consecutive repeats of the surface-layer homology (SLH) domain to engage secondary cell wall polysaccharides (SCWP). Using x-ray crystallography, we reveal here the structure of these SLH domains, which assume the shape of a three-prong spindle. Each SLH domain contributes to a three-helical bundle at the spindle base, whereas another ?-helix and its connecting loops generate the three prongs. The inter-prong grooves contain conserved cationic and anionic residues, which are necessary for SLH domains to bind the B. anthracis SCWP. Modeling experiments suggest that the SLH domains of other S-layer proteins also fold into three-prong spindles and capture bacterial envelope carbohydrates by a similar mechanism.The Journal of biological chemistryStructure of surface layer homology (SLH) domains from Bacillus anthracis surface array protein.PMC3138252GM0071831-U54-AI-057153U54 GM074942AI69227GM074942U54 GM094585R01 AI069227Kern JSchneewind OJoachimiak ABinkowski TAWilton RZhang RfalseStructure of surface layer homology (SLH) domains from Bacillus anthracis surface array protein.Surface (S)-layers, para-crystalline arrays of protein, are deposited in the envelope of most bacterial species. These surface organelles are retained in the bacterial envelope through the non-covalent association of proteins with cell wall carbohydrates. Bacillus anthracis, a Gram-positive pathogen, produces S-layers of the protein Sap, which uses three consecutive repeats of the surface-layer homology (SLH) domain to engage secondary cell wall polysaccharides (SCWP). Using x-ray crystallography, we reveal here the structure of these SLH domains, which assume the shape of a three-prong spindle. Each SLH domain contributes to a three-helical bundle at the spindle base, whereas another ?-helix and its connecting loops generate the three prongs. The inter-prong grooves contain conserved cationic and anionic residues, which are necessary for SLH domains to bind the B. anthracis SCWP. Modeling experiments suggest that the SLH domains of other S-layer proteins also fold into three-prong spindles and capture bacterial envelope carbohydrates by a similar mechanism.2011-01-01T00:00:00Z2011 Jul2021-02-19T23:30:52Z2019-03-27T03:07:10ZS-EPMC31382522157203910.1074/jbc.M111.24807010.1074/jbc.m111.248070