Citrobacter rodentium possesses a functional type II secretion system necessary for successful host infection

Infectious diarrheal diseases are the third leading cause of mortality in young children, many of which are driven by Gram-negative bacterial pathogens. To establish successful host infections these pathogens employ a plethora of virulence factors necessary to compete with the resident microbiota, and evade and subvert the host defenses. The type II secretion system (T2SS) is one such conserved molecular machine that allows for the delivery of effector proteins into the extracellular milieu. To explore the role of the T2SS during natural host infection, we used Citrobacter rodentium, a murine enteric pathogen, as a model of human intestinal disease caused by pathogenic Escherichia coli such as Enteropathogenic and Enterohemorrhagic E. coli (EPEC and EHEC). In this study, we determined that the C. rodentium genome encodes one T2SS and 22 potential T2SS-secreted protein effectors, as predicted via sequence homology. We demonstrated that this system was functional in vitro, identifying a role in intestinal mucin degradation allowing for its utilization as a carbon source, and promoting C. rodentium attachment to a mucus-producing colon cell line. During host infection, loss of the T2SS or associated effectors led to a significant colonization defect and lack of systemic spread. In mice susceptible to lethal infection, T2SS-deficient C. rodentium was strongly attenuated, resulting in reduced morbidity and mortality in infected hosts. Together these data highlight the important role of the T2SS and its effector repertoire during C. rodentium pathogenesis, aiding in successful host mucosal colonization.

Characterization and regulation of Leishmania major 3-hydroxy-3-methylglutaryl-CoA reductase

In eukaryotes the enzyme 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase catalyses the synthesis of mevalonic acid, a common precursor to all isoprenoid compounds. Here we report the isolation and overexpression of the gene coding for HMG-CoA reductase from Leishmania major. The protein from Leishmania lacks the membrane domain characteristic of eukaryotic cells but exhibits sequence similarity with eukaryotic reductases. Highly purified protein was achieved by ammonium sulphate precipitation followed by chromatography on hydroxyapatite. Kinetic parameters were determined for the protozoan reductase, obtaining K(m) values for the overall reaction of 40.3+/-5.8 microM for (R,S)-HMG-CoA and 81.4+/-5.3 microM for NADPH; V(max) was 33.55+/-1.8 units x mg(-1). Gel-filtration experiments suggested an apparent molecular mass of 184 kDa with subunits of 46 kDa. Finally, in order to achieve a better understanding of the role of this enzyme in trypanosomatids, the effect of possible regulators of isoprenoid biosynthesis in cultured promastigote cells was studied. Neither mevalonic acid nor serum sterols appear to modulate enzyme activity whereas incubation with lovastatin results in significant increases in the amount of reductase protein. Western- and Northern-blot analyses indicate that this activation is apparently performed via post-transcriptional control.

A soluble 3-hydroxy-3-methylglutaryl-CoA reductase in the protozoan Trypanosoma cruzi

We report the isolation and characterization of a genomic clone containing the open reading frame sequence for 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase from Trypanosoma cruzi, the causative agent of Chagas' disease. The protozoan gene encoded for a smaller polypeptide than the rest of the genes described from eukaryotic organisms and the deduced amino acid sequence could be aligned with the C-terminal half of animal and plant reductases exhibiting pronounced similarity to other eukaryotic counterparts. Further examination of the 5' flanking region by cDNA analysis and establishment of the splice acceptor sites clearly indicated that the corresponding mRNA apparently lacks sequences encoding a membrane N-terminal domain. The reductase gene is a single copy and is located on a chromosome of 1.36 Mb as determined by contour-clamped homogeneous electric field electrophoresis. The overall cellular distribution of enzymic activity was investigated after differential centrifugation of Trypanosoma cell extracts. Reductase activity was primarily associated with the cellular soluble fraction because 95% of the total cellular activity was recovered in the supernatant and was particularly sensitive to proteolytic inactivation. Furthermore the enzyme can be efficiently overexpressed in a highly active form by using the expression vector pET-11c. Thus Trypanosoma cruzi HMG-CoA reductase is unique in the sense that it totally lacks the membrane-spanning sequences present in all eukaryotic HMG-CoA reductases so far characterized.