Cloning and characterization of three cheB genes in Leptospira interrogans

The molecular basis of leptospiral pathogenesis

The mechanisms of disease pathogenesis in leptospirosis are poorly defined. Recent developments in the application of genetic tools in the study of Leptospira have advanced our understanding by allowing the assessment of mutants in animal models. As a result, a small number of essential virulence factors have been identified, though most do not have a clearly defined function. Significant advances have also been made in the in vitro characterization of leptospiral interaction with host structures, including extracellular matrix proteins (such as laminin, elastin, fibronectin, collagens), proteins related to hemostasis (fibrinogen, plasmin), and soluble mediators of complement resistance (factor H, C4b-binding protein), although none of these in vitro findings has been translated to the host animal. Binding to host structures may permit colonization of the host, prevention of blood clotting may contribute to hemorrhage, while interaction with complement resistance mediators may contribute to survival in serum. While not a classical intracellular pathogen, the interaction of leptospires and phagocytic cells appears complex, with bacteria surviving uptake and promoting apoptosis; mutants relating to these processes (such as cell invasion and oxidative stress resistance) are attenuated in vivo. Another feature of leptospiral biology is the high degree of functional redundancy and the surprising lack of attenuation of mutants in what appear to be certain virulence factors, such as LipL32 and LigB. While many advances have been made, there remains a lack of understanding of how Leptospira causes tissue pathology. It is likely that leptospires have many novel pathogenesis mechanisms that are yet to be identified.

Genetic and molecular biological characterization of two homologous cheR genes from Leptospira interrogans

The Leptospira interrogans genome encodes two copies of cheR genes and each of them is able to complement for the swarming defective phenotype of Escherichia coli cheR null mutant RP1254 to certain extent, while over-expression of either of them inhibits the swarming of the chemotactic wild-type E. coli strain, RP437. Therefore, both CheR1 and CheR2 ought to bear the methyltransferase activities, although CheR1 has only one instead of two conserved basic amino acid residues located on the positively charged face of α2-helix. When this residue as well as the Lys48 and Arg55 of CheR2 was mutated, none of the CheRs was able to maintain aforementioned complementation functions, suggesting their critical roles in recognition of methyl-accepting chemotaxis proteins similar to that of E. coli. Demonstrated by microarray assay, the expression of cheR1 in L. interrogans cultured at 28°C in Ellinghausen-McCullough-Johnson-Harris medium was significantly lower than the average transcription level of all other genes, while the transcription of cheR2 was significantly higher than that of cheR1 in accordance with real-time reverse transcriptase-polymerase chain reaction assay. Tandem MS-MS data mining for the proteome of the same culture detected 16 peptides derived from CheR2 but none from CheR1. Therefore, although both genes were shown to be functional in E. coli, the structurally more conserved CheR2 rather than CheR1 might be the major functional component of L. interrogans chemotaxis adaptation system under our laboratory culture conditions.

Leptospira interrogans encodes an ROK family glucokinase involved in a cryptic glucose utilization pathway

Although Leptospira interrogans is unable to utilize glucose as its carbon/energy source, the LA_1437 gene of L. interrogans serovar Lai potentially encodes a group III glucokinase (GLK). The L. interrogans GLK (LiGLK) heterogeneously expressed in Escherichia coli was purified and proved to be a homodimeric enzyme with its specific activity of 12.3 ± 0.6 U/mg x protein determined under an improved assay condition (pH 9.0, 50 ° C), 7.5-fold higher than that assayed under the previously used condition (pH 7.3, 25 ° C). The improved sensitivity allowed us to detect this enzymatic activity of (5.0 ± 0.6) × 10(-3) U/mg x protein in the crude extract of L. interrogans serovar Lai cultured in standard Ellinghausen-McCullough-Johnson-Harris medium. The k(cat) and K(m) values for d-glucose and ATP were similar to those of other group III GLKs, although the K(m) value for ATP was slightly higher. Site-directed mutagenesis analysis targeting the conserved amino acid residues in the potential ATP-binding motif hinted that a proper array of Gly residues in the motif might be important for maintaining the conformation that was essential for its function. Gene expression profiling and quantitative proteomic data mining provided preliminary evidence for the absence of efficient systems involved in glucose transport and glycolysis that might account for the failure of glucose utilization in L. interrogans.