title: Structure of surface layer homology (SLH) domains from Bacillus anthracis surface array protein.
abstract: 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 α-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.
authors.affiliation: Department of Microbiology, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Kern
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Wilton
authors.forename: Rongguang
authors.initials: R
authors.lastname: Zhang
authors.forename: T Andrew
authors.initials: TA
authors.lastname: Binkowski
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
authors.forename: Olaf
authors.initials: O
authors.lastname: Schneewind
mesh_terms: D000595:Amino Acid Sequence; D001408:Bacillus anthracis; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; D011135:Polysaccharides, Bacterial; C055764:S-layer proteins