Role of oligopeptidase B in <i>Salmonella</i> pathogeneis, and, Molecular characterization of the <i>Leishmania amazonensis</i> iron transporter, LIT1
Salmonella typhimurium and Leishmania are responsible for the human infections salmonellosis and leishmaniasis, respectively. In this study we examine the role of oligopeptidase B in Salmonella pathogenesis as well as investigate the amino acid residues and metal binding motifs within the Leishmania iron transporter that are critical for translocating iron into the parasite.
Oligopeptidase B (opdB) has been shown to be critical for parasite entry into mammalian cells and for the virulence of Trypanosoma cruzi (Caler et al., 1998). It has also been shown to contribute to the pathogenesis of T. brucei and T. evansi, in the blood stream of the mammalian host (Morty et al., 2001), (Morty et al., 2005) and (Troeberg et al., 1996). Although this enzyme exists in Salmonella , its role in the pathogenicity of this pathogen has not been determined. To examine the role of opdB in Salmonella pathogenesis, the opdB gene was deleted from the genome of Salmonella typhimurium . The null mutant was examined for its ability to acquire nutrients in defined medium, to invade and replicate within both intestinal epithelial cells and murine bone marrow derived macrophages, and to regulate Salmonella-induced programmed death of macrophages. The data suggest that oligopeptidase B is not required for the acquisition of nutrients during growth of Salmonella in defined medium, nor is it important for the invasion and replication of the pathogen within mammalian cells. It also does not participate in the regulation of Salmonella-induced programmed death of macrophages. Thus, although oligopeptidase B is expressed in Salmonella, it does not appear to be required for any of the known virulence properties of this pathogen.
The second part of this study involved a novel iron transporter recently identified in Leishmania amazonensis, and shown to be essential for full virulence of this parasite. To functionally characterize this transporter, we mutagenized and created truncated forms of the protein to identify residues that are critical for iron transport. We have placed these mutant constructs within the mutant yeast strain, fet3fet4, which lacks both a high and low affinity ferrous iron transporter, in order to examine the ability of the mutant proteins to reconstitute the incapacity of this strain to grow in iron-limiting conditions, as well as to transport iron. The data revealed that residues Hist-108, Glu-112, Asp-263, Hist-283, Ser-284, Hist-309, and Glu-313 are vital for the function of the Leishmania iron transporter (LIT1). In contrast to its homologue IRT1 found in Arabidopsis thaliana, Tyr-382 and Asp-391 of LIT1 are only essential for metal transport in yeast. We also determined that LIT1 contains an extra intracellular domain with a HxHxH motif, that appears to function as an essential metal binding site. Collectively this study has functionally characterized the first iron transporter to have been identified in Leishmania.