Structural and functional dissection reveals distinct roles of Ca2+-binding sites in the giant adhesin SiiE of Salmonella enterica

PLoS Pathogens

Britta Peters¹  Johanna Stein¹  Michael Hensel¹  Nathalie Sander¹  Achim Sandmann²  Heinrich Sticht²  Stefan Klingl³  Yves A. Muller³  Nicola Taccardi⁴  Roman G. Gerlach⁵ 

[1] Abt. Mikrobiologie, Universität Osnabrück, Osnabrück, Germany;Institut für Biochemie, FAU Erlangen-Nürnberg, Erlangen, Germany;Lehrstuhl für Biotechnik, FAU Erlangen-Nürnberg, Erlangen, Germany;Lehrstuhl für Chemische Reaktionstechnik, FAU Erlangen-Nürnberg, Erlangen, Germany;Robert-Koch-Institut, Wernigerode, Germany

关键词: Secretion;    Secretion systems;    Adhesins;    Protein secretion;    Crystal structure;    Salmonella;    Mutant strains;    Tryptophan;   

DOI  :  10.1371/journal.ppat.1006418

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

The giant non-fimbrial adhesin SiiE of Salmonella enterica mediates the first contact to the apical site of epithelial cells and enables subsequent invasion. SiiE is a 595 kDa protein composed of 53 repetitive bacterial immunoglobulin (BIg) domains and the only known substrate of the SPI4-encoded type 1 secretion system (T1SS). The crystal structure of BIg50-52 of SiiE revealed two distinct Ca2+-binding sites per BIg domain formed by conserved aspartate or glutamate residues. In a mutational analysis Ca2+-binding sites were disrupted by aspartate to serine exchange at various positions in the BIg domains of SiiE. Amounts of secreted SiiE diminish with a decreasing number of intact Ca2+-binding sites. BIg domains of SiiE contain distinct Ca2+-binding sites, with type I sites being similar to other T1SS-secreted proteins and type II sites newly identified in SiiE. We functionally and structurally dissected the roles of type I and type II Ca2+-binding sites in SiiE, as well as the importance of Ca2+-binding sites in various positions of SiiE. Type I Ca2+-binding sites were critical for efficient secretion of SiiE and a decreasing number of type I sites correlated with reduced secretion. Type II sites were less important for secretion, stability and surface expression of SiiE, however integrity of type II sites in the C-terminal portion was required for the function of SiiE in mediating adhesion and invasion.

【 授权许可】

CC BY