The Salmonella typhimurium virulence plasmid complement resistance gene rck is homologous to a family of virulence-related outer membrane protein genes, including pagC and ail

Abstract

A fragment of the Salmonella typhimurium virulence plasmid containing the rck locus, when cloned in the recombinant cosmid pADE016, was shown previously to confer high-level complement resistance on both rough and smooth Escherichia coli, SalmoneUa minnesota, and S. typhimurium and was associated with the production of an outer membrane protein. The outer membrane proteins (OMPs) of gram-negative bacteria provide specialized functions enabling the organisms to interact with the environment, promoting survival. For pathogenic bacteria, a number of specific proteins required for virulence are located in the outer membrane. Gram-negative organisms causing invasive disease must resist the bactericidal action of complement present in normal human serum (22,46). The outer membrane is the initial site of interaction between complement and the bacterial cell, and both the structure of the lipopolysaccharide (LPS) and the presence of specific OMPs have been shown to be critical determinants of bacterial resistance to complement (22). In Salmonella spp., the number and length of the LPS side chains (O antigen) play a major role in complement resistance, since long-chain LPS leads to complement activation at a distance from the cell surface and precludes insertion of the membrane attack complex in the outer membrane (23, 24).Several genes encoded by Salmonella virulence plasmids have been implicated in serum resistance. These plasmids, 50 to 100 kb in size, are present in several invasive Salmonella serotypes, and all appear to contain a common 8.4-kb region required for progressive infection of the reticuloendothelial system, leading to septicemia and death in experimental animals (14). Genetic loci specifying serum resistance map outside this core virulence region and include a traT allele (42), a determinant affecting LPS structure (26), and the rsk region, which enhances the ability of smooth S. typhimurium to grow in serum when the virulence plasmid is integrated in the chromosome (50, 51).A distinct complement resistance locus was cloned from the S. typhimurium virulence plasmid by J. Hackett and colleagues (15). These workers showed that pADE016, containing a 2.4-kb ClaI-PstI fragment in a multicopy cosmid vector, confers high-level complement resistance to a serumsensitive Escherichia coli K-12 strain and to the rough, plasmid-cured S. typhimurium derivative of the wild-type parent strain (15). In addition, they found that expression of the serum resistance phenotype by pADE016 was associated with the production of an OMP. We have recently investigated the mechanisms by which this locus (designated rck, for resistance to complement killing) mediates serum resistance in gram-negative bacteria (17). These studies suggest that the rck gene product prevents complement-mediated bacteriolysis by inhibiting effective insertion of the terminal C5b-9 membrane attack complex into the gram-negative outer membrane, a mechanism of complement resistance similar to that noted in serum-resistant strains of Neisseria gonorrhoeae (2...

Rck of Salmonella enterica, subspecies enterica serovar Enteritidis, mediates Zipper-like internalization

“…The pagN gene is activated by PhoP and the corresponding protein shares identities with the Hek and Tia invasins/ adhesins of pathogenic E. coli [7]. The Rck protein is encoded by different serovars, including Salmonella Enteritidis and Salmonella Typhimurium, and is a member of a 17-to 19-kDa OMP family involved in cell adhesion and/or invasion including Ail (Yersinia enterocolitica), PagC (Salmonella Typhimurium), OmpX (Enterobacter cloacae) and Lom (bacteriophage lambda-lysogenic E. coli) [11]. Heffernan et al [6] have previously shown that Rck overexpressed in a non-invasive E. coli strain enables the bacteria to adhere to and invade fibroblastic cells.…”

“…In addition to adhesion and entry capabilities, Rck also confers a high level of resistance to the bactericidal activity of complement, independent of the lipopolysaccharide (LPS) structure, by inhibiting the polymerization of complement component C9 in the bacterial membrane [9,10]. Rck belongs to a family of five homologous OMP proteins characterized in Salmonella (Rck and PagC), Escherichia coli (Lom), Yersinia enterocolitica (Ail) and Enterobacter cloacae (OmpX) [11]. Molecular analysis has shown that Rck is homologous to PagC and Ail with 53% and 48% identity, respectively, but complement resistance and invasion have been attributed only to Rck and Ail [11].…”

“…Rck belongs to a family of five homologous OMP proteins characterized in Salmonella (Rck and PagC), Escherichia coli (Lom), Yersinia enterocolitica (Ail) and Enterobacter cloacae (OmpX) [11]. Molecular analysis has shown that Rck is homologous to PagC and Ail with 53% and 48% identity, respectively, but complement resistance and invasion have been attributed only to Rck and Ail [11]. However, the precise role of Rck in Salmonella invasion process is still unknown, as well as the mechanism of the Rck-dependent internalization pathway.…”

Phenotypic characterization of OmpX, an Ail homologue of Yersinia pestis KIM

“…One Omp, OmpX, was first described for Enterobacter cloacae (Stoorvogel et al, 1991), but homologues, including PagC, Lom, Rck and Ail (the attachment-invasion locus protein of Yersinia spp. ), were identified in other Gram-negative bacteria (Dupont et al, 2004;Heffernan et al, 1992a;Mecsas et al, 1995). Proteins in this family promote invasion, resistance to complementmediated killing, survival in macrophages, and internalization in epithelial cells (Cirillo et al, 1996).…”

Functional Recruitment of the Human Complement Inhibitor C4BP to Yersinia pseudotuberculosis Outer Membrane Protein Ail

“…Ail belongs to a family of highly conserved 17-19-kDa outer membrane proteins found in the Enterobacteriaceae, including Rck (Salmonella typhimurium and enteritidis), PagC (typhoid and nontyphoid Salmonella, Escherichia coli O157:H7), and OmpX (E. coli and Enterobacter cloacae) (13,14). All of these proteins have virulence-associated phenotypes.…”