The roles of flagellar secretion, SopB ubiquitination, and SopA in Salmonella pathogenesis

Wendy Maile Higashide, Purdue University

Abstract

Salmonella spp. are Gram-negative bacteria that cause gastroenteritis and enteric fever in a variety of mammalian, avian, and reptile hosts. In order to cause disease, Salmonella directs the transport of its proteins (termed “effectors”) into the host cell cytoplasm by Salmonella-encoded type III secretion systems (TTSS) called SPI-1 and SPI-2 TTSS. These translocated bacterial proteins are then able to alter such basic host-cell functions as signal transduction, cytoskeletal architecture, membrane trafficking, and cytokine gene expression. One of the proteins that is translocated into the host cell is Salmonella outer protein A (SopA). SopA has been found to be involved in inducing the inflammatory and secretory responses that are associated with gastroenteritis. We have determined that the N-terminal 45 amino acid residues of SopA are necessary and sufficient for directing its secretion and translocation into the host cell. SopA1-45, but not SopA1-44, is also able to bind to its chaperone, InvB, indicating that SPI-1 type III secretion and translocation of SopA require its chaperone. We have determined that SopA interacts with a host protein called HsRMA1. HsRMA1 is an ubiquitin E3 ligase of the host ubiquitination system. The ubiquitination of SopA by HsRMA1 has been found to result in SopA’s degradation. It was determined that a sopA mutant escapes out of the Salmonella-containing vacuoles less frequently to the cytosol than wild type Salmonella in Hela cells in a HsRMA1-dependent manner. Our data suggest that efficient bacterial escape into the cytosol of epithelial cells requires HsRMA1- mediated SopA ubiquitination. Additional interaction studies have determined that SopA interacts with another E3 ligase called Mib2. Mib2 is an E3 ligase found to activate the NF-κB pathway, which leads to the inflammatory response. We have also found have found that SPI-1 TTSS proteins are secreted aberrantly through the flagellar export apparatus, which is involved in the biogenesis of flagellum. Unlike the SPI-1 TTSS, however, the flagellar export apparatus is not able to translocate these proteins into the host cell. In addition, studies have found that the ubiquitination of Salmonella protein, SopB, is not necessary for its roles in Salmonella invasion and Akt activation.

Degree

Ph.D.

Advisors

Zhou, Purdue University.

Subject Area

Microbiology

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