SiiA and SiiB are novel type I secretion system subunits controlling SPI4-mediated adhesion of Salmonella enterica.

The giant non-fimbrial adhesin SiiE is essential to establish intimate contact between Salmonella enterica and the apical surface of polarized epithelial cells. SiiE is secreted by a type I secretion system (T1SS) encoded by Salmonella Pathogenicity Island 4 (SPI4). We identified SiiA and SiiB as two regulatory proteins encoded by SPI4. Mutant strains in siiA or siiB still secrete SiiE, but are highly reduced in adhesion to, and invasion of polarized cells. SiiA and SiiB are inner membrane proteins with one and three transmembrane (TM) helices respectively. TM2 and TM3 of SiiB are similar to members of the ExbB/TolQ family, while the TM of SiiA is similar to MotB and a conserved aspartate residue in this TM is essential for SPI4-encoded T1SS function. Co-immunoprecipitation, bacterial two-hybrid and FRET demonstrate homo- and heterotypic protein interactions for SiiA and SiiB. SiiB, but not SiiA also interacts with the SPI4-T1SS ATPase SiiF. The integrity of the Walker A box in SiiF was required for SiiB-SiiF interactionand SiiF dimer formation. Based on these data, we describe SiiA and SiiB as new, exclusively virulence-associated members of the Mot/Exb/Tol family of membrane proteins. Both proteins are involved in a novel mechanism of controlling SPI4-T1SS-dependent adhesion, most likely by formation of a proton-conducting channel.

Wille T ，Wagner C ，Mittelstädt W ，Blank K ，Sommer E ，Malengo G ，Döhler D ，Lange A ，Sourjik V ，Hensel M ，Gerlach RG ... -  《-》

Structural and functional characterization of SiiA, an auxiliary protein from the SPI4-encoded type 1 secretion system from Salmonella enterica.

Salmonella invasion is mediated by a concerted action of the Salmonella pathogenicity island 4 (SPI4)-encoded type one secretion system (T1SS) and the SPI1-encoded type three secretion system (T3SS-1). The SPI4-encoded T1SS consists of five proteins (SiiABCDF) and secretes the giant adhesin SiiE. Here, we investigated structure-function relationships in SiiA, a non-canonical T1SS subunit. We show that SiiA consists of a membrane domain, an intrinsically disordered periplasmic linker region and a folded globular periplasmic domain (SiiA-PD). The crystal structure of SiiA-PD displays homology to that of MotB and other peptidoglycan (PG)-binding domains. SiiA-PD binds PG in vitro, albeit at an acidic pH, only. Mutation of Arg162 impedes PG binding of SiiA and reduces Salmonella invasion efficacy. SiiA forms a complex with SiiB at the inner membrane (IM), and the observed SiiA-MotB homology is paralleled by a predicted SiiB-MotA homology. We show that, similar to MotAB, SiiAB translocates protons across the IM. Mutating Asp13 in SiiA impairs proton translocation. Overall, SiiA shares numerous properties with MotB. However, MotAB uses the proton motif force (PMF) to energize the bacterial flagellum, it remains to be shown how usage of the PMF by SiiAB assists T1SS function and Salmonella invasion.

Kirchweger P ，Weiler S ，Egerer-Sieber C ，Blasl AT ，Hoffmann S ，Schmidt C ，Sander N ，Merker D ，Gerlach RG ，Hensel M ，Muller YA ... -  《-》

Coordinate regulation of Salmonella pathogenicity island 1 (SPI1) and SPI4 in Salmonella enterica serovar Typhimurium.

Main-Hester KL ，Colpitts KM ，Thomas GA ，Fang FC ，Libby SJ ... -  《-》

Salmonella Pathogenicity Island 4 encodes a giant non-fimbrial adhesin and the cognate type 1 secretion system.

Gerlach RG ，Jäckel D ，Stecher B ，Wagner C ，Lupas A ，Hardt WD ，Hensel M ... -  《CELLULAR MICROBIOLOGY》

Salmonella pathogenicity island 4-mediated adhesion is coregulated with invasion genes in Salmonella enterica.

Gerlach RG ，Jäckel D ，Geymeier N ，Hensel M ... -  《-》