Functional dissection of SiiE, a giant non-fimbrial adhesin of Salmonella enterica.

Salmonella enterica deploys the giant non-fimbrial adhesin SiiE to adhere to the apical side of polarized epithelial cells. The establishment of close contact is a prerequisite for subsequent invasion mediated by translocation of effector proteins of the Salmonella Pathogenicity Island 1 (SPI1)-encoded type III secretion system (T3SS). Although SiiE is secreted into the culture medium, the adhesin is retained on the bacterial envelope in the phase of highest bacterial invasiveness. To dissect the structural requirements for secretion, retention and adhesive properties, comprehensive deletional and functional analyses of various domains of SiiE were performed. We observed that β-sheet and coiled-coil domains in the N-terminal moiety of SiiE are required for the control of SiiE retention on the surface and co-ordinated release. These results indicate a novel molecular mechanism for the control of surface display of a T1SS-secreted adhesin that acts cooperatively with the SPI1-T3SS.

Wagner C ，Polke M ，Gerlach RG ，Linke D ，Stierhof YD ，Schwarz H ，Hensel M ... -  《-》

The Salmonella enterica giant adhesin SiiE binds to polarized epithelial cells in a lectin-like manner.

The invasion of polarized epithelial cells by Salmonella enterica requires the cooperative activity of the Salmonella pathogenicity island (SPI) 1-encoded type III secretion system (T3SS) and the SPI4-encoded giant non-fimbrial adhesin SiiE. SiiE is a highly repetitive protein composed of 53 bacterial Ig (BIg) domains and mediates binding to the apical side of polarized epithelial cells. We analysed the binding properties of SiiE and observed lectin-like activity. SiiE-dependent cell invasion can be ablated by chemical or enzymatic deglycosylation. Lectin blockade experiments revealed that SiiE binding is specific for glycostructures with terminal N-acetyl-glucosamine (GlcNAc) and/or α 2,3-linked sialic acid. In line with these data, we found that SiiE-expressing Salmonella bind to the GlcNAc polymer chitin. Various recombinant SiiE fragments were analysed for host cell binding. We observed that C-terminal portions of SiiE bind to the apical side of polarized cells and the intensity of binding increases with the number of BIg domains present in the recombinant proteins. Based on these results, we propose that SiiE mediates multiple interactions per molecule with glycoproteins and/or glycosylated phospholipids present in the apical membrane of polarized epithelial cells. Thisintimate binding enables the subsequent function of the SPI1-T3SS, resulting in host cell invasion.

Wagner C ，Barlag B ，Gerlach RG ，Deiwick J ，Hensel M ... -  《-》

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》

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

Peters B ，Stein J ，Klingl S ，Sander N ，Sandmann A ，Taccardi N ，Sticht H ，Gerlach RG ，Muller YA ，Hensel M ... -  《-》

The giant adhesin SiiE of Salmonella enterica.

Barlag B ，Hensel M 《-》