Listeria monocytogenes expresses surface proteins covalently anchored to the
peptidoglycan by sortase
enzymes. Inactivation of srtA
attenuates Listeria 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 an srtA
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 of
L. monocytogenes strains and absent from all other
Listeria species, inlI (lmo0333) and inlJ (lmo2821). They also revealed two other LPXTG protein-encoding genes, ORF29 and ORF2568, present only in a subclass of
L. monocytogenes serovars, including the
epidemic serovar 4b. We report here that an inlJ deletion
mutant, in contrast to inlI and ORF29
mutants, is significantly
attenuated in
virulence after
intravenous infection of
mice or oral
inoculation of hEcad
mice. Interestingly, a DeltaORF2568 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 in
L. monocytogenes.
