title: Structural insights into the molecular organization of the S-layer from Clostridium difficile.
abstract: Clostridium difficile expresses a surface layer (S-layer) which coats the surface of the bacterium and acts as an adhesin facilitating interaction of the bacterium with host enteric cells. The S-layer contains a high-molecular-weight S-layer protein (HMW SLP) and its low-molecular-weight partner protein (LMW SLP). We show that these proteins form a tightly associated non-covalent complex, the H/L complex, and we identify the regions of both proteins responsible for complex formation. The 2.4 A X-ray crystal structure of a truncated derivative of the LMW SLP reveals two domains. Domain 1 has a two-layer sandwich architecture while domain 2, predicted to orientate towards the external environment, contains a novel fold. Small-angle X-ray scattering analysis of the H/L complex shows an elongated molecule, with the two SLPs arranged 'end-to-end' interacting with each other through a small contact area. Alignment of LMW SLPs, which exhibit high sequence diversity, reveals a core of conserved residues that could reflect functional conservation, while allowing for immune evasion through sequence variation. These structures are the first described for the S-layer of a bacterial pathogen, and provide insights into the assembly and biogenesis of the S-layer.
authors.affiliation: Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW72AZ, UK.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Fagan
authors.forename: David
authors.initials: D
authors.lastname: Albesa-Jové
authors.forename: Omar
authors.initials: O
authors.lastname: Qazi
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Brown
authors.forename: Neil F
authors.initials: NF
authors.lastname: Fairweather
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D016360:Clostridioides difficile / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins