Identification and type III-dependent secretion of the Yersinia pestis insecticidal-like proteins.

Plague, or the Black Death, is a zoonotic disease that is spread from mammal to mammal by fleas. This mode of transmission demands that the causative agent of this disease, Yersinia pestis, is able to survive and multiply in both mammals and insects. In recent years the complete genome sequence of a number of Y. pestis strains have been determined. This sequence information indicates that Y. pestis contains a cluster of genes with homology to insecticidal toxin encoding genes of the insect pathogen Photorhabdus luminescens. Here we demonstrate that Y. pestis KIM strains produced the encoded proteins. Production of the locus-encoded proteins was dependent on a gene (yitR) encoding a member of the LysR family of transcriptional activators. Evidence suggests the proteins are type III secretion substrates. N terminal amino acids (100 to 367) of each protein fused to an epitope tag were secreted by the virulence plasmid type III secretion type. A fusion protein comprised of the N-terminus of YipB and the enzymatic active component of Bordetella pertussis adenylate cyclase (Cya) was translocated into both mammalian and insect cells. In conclusion, a new class of Y. pestis type III secreted and translocated proteins has been identified. We hypothesize that these proteins function to promote transmission of and infection by Y. pestis.