title: Structural insight into the giant Ca²⁺-binding adhesin SiiE: implications for the adhesion of Salmonella enterica to polarized epithelial cells.
abstract: SiiE from Salmonella enterica is a giant 5,559-residue-long nonfimbrial adhesin that is secreted by a type 1 secretion system (T1SS) and initiates bacterial adhesion to polarized host cells. Structural insight has been gained into the 53 bacterial Ig-like (BIg) domains of SiiE, which account for 94% of the entire SiiE sequence. The crystal structure of a fragment comprising BIg domains 50 to 52 of SiiE reveals the BIg domain architecture and highlights two types of SiiE-specific Ca²⁺-binding sites. Sequence homology considerations suggest that full-length SiiE interacts with more than 100 Ca²⁺ ions. Molecular dynamics simulations and single-molecule imaging indicate that Ca²⁺ binding confers SiiE with a rigid 200 nm rod-like habitus that is required to reach out beyond the Salmonella lipopolysaccharide layer and to promote adhesion to host cells. The crystal structure suggests plausible routes for the establishment of the initial contact between Salmonella and host cells.
authors.affiliation: Lehrstuhl für Biotechnik, Department of Biology, Friedrich-Alexander-University of Erlangen-Nuremberg, 91054 Erlangen, Germany.
authors.forename: Martin H
authors.initials: MH
authors.lastname: Griessl
authors.forename: Benedikt
authors.initials: B
authors.lastname: Schmid
authors.forename: Kristin
authors.initials: K
authors.lastname: Kassler
authors.forename: Christoph
authors.initials: C
authors.lastname: Braunsmann
authors.forename: Regina
authors.initials: R
authors.lastname: Ritter
authors.forename: Britta
authors.initials: B
authors.lastname: Barlag
authors.forename: York-Dieter
authors.initials: YD
authors.lastname: Stierhof
authors.forename: Karina U
authors.initials: KU
authors.lastname: Sturm
authors.forename: Claudia
authors.initials: C
authors.lastname: Danzer
authors.forename: Carolin
authors.initials: C
authors.lastname: Wagner
authors.forename: Tilman E
authors.initials: TE
authors.lastname: Schäffer
authors.forename: Heinrich
authors.initials: H
authors.lastname: Sticht
authors.forename: Michael
authors.initials: M
authors.lastname: Hensel
authors.forename: Yves A
authors.initials: YA
authors.lastname: Muller
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D016764:Cell Polarity; D004847:Epithelial Cells / Q000378:metabolism*; D011487:Protein Conformation; D019779:Salmonella enterica / Q000737:chemistry* / Q000378:metabolism
chemical_list: D018829:Adhesins, Bacterial; D002135:Calcium-Binding Proteins