LPXTG Protein InlJ, a Newly Identified Internalin Involved in Listeria monocytogenes Virulence

Listeria monocytogenes expresses surface proteins covalently anchored to the peptidoglycan by sortase enzymes. Inactivation ofsrtA attenuatesListeria virulence in mice (H. Bierne, S. K. Mazmanian, M. Trost, M. G. Pucciarelli, G. Liu, P. Dehoux, L. Jansch, F. Garcia-del Portillo, O. Schneewind, and P. Cossart, Mol. Microbiol.43: 869-881, 2002). We show here that ansrtA mutant is more attenuated than an internalin mutant in orally infected guinea pigs and transgenic mice expressing human E-cadherin (hEcad mice), indicating the involvement of other SrtA substrates, LPXTG proteins, in food-borne listeriosis. Data recently generated with a listerial DNA macroarray identified two LPXTG protein-encoding genes present in the genomes ofL. monocytogenes strains and absent from all otherListeria species,inlI (lmo0333) andinlJ (lmo2821). They also revealed two other LPXTG protein-encoding genes, ORF29 and ORF2568, present only in a subclass ofL. monocytogenes serovars, including the epidemic serovar 4b. We report here that aninlJ deletion mutant, in contrast toinlI and ORF29 mutants, is significantly attenuated in virulence after intravenous infection of mice or oral inoculation of hEcad mice. Interestingly, a ΔORF2568 strain showed a slight increase in virulence.inlJ encodes a leucine-rich repeat (LRR) protein that is structurally related to the listerial invasion factor internalin. However, the consensus sequence of the InlJ LRR defines a novel subfamily of cysteine-containing LRRs in bacteria. In conclusion, this postgenomic approach identified InlJ as a new virulence factor among the proteins belonging to the internalin family inL. monocytogenes .