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The Yersinia Protein YpkA

Nearly 200 million people are estimated to have died in the plague epidemics that devastated the ancient world, and the successful weaponization of plague in the former Soviet Union bioweapons program has made this pathogen a primary biodefense concern. Additional medical concerns arise from the evolution of multi-drug resistant strains of the plague bacterium that have been reported in several locations from patient isolates. The plague is caused by the bacterial pathogen Yersinia pestis, which along with the food-borne agents of gastroenteritis, Y. enterocolitica and Y. pseudotuberculosis, share the highly conserved Yersinia virulence plasmid, or pYV, which is necessary to cause disease. This plasmid harbors numerous genes, a large number of which are associated with a type III protein secretion system (T3SS) that confers the ability of diverse pathogens to deliver virulence factors into host cells. The translocated virulence factors of Yersinia include a protein tyrosine phosphatase, a cysteine protease, and a GTPase activating protein, among others, and collaborate to disrupt and impair the normal cytoskeletal regulation in macrophages and polymorphonuclear neutrophils (PMNs) to achieve an anti-phagocytic effect.

An important virulence factor of Yersinia spp. is the Yersinia protein kinase A, or YpkA (also called YopO in Y. enterocolitica), a substrate of the T3SS which was first identified through its important contribution to disease progression and a region of sequence homology to eukaryotic serine/threonine kinases. Y. pseudotuberculosis mutants with disruptions in YpkA have shown severely attenuated virulence in mouse infection models. YpkA is an 82kD multi-domain protein, which, in addition to the protein kinase, possesses a domain that binds to the small GTPases RhoA and Rac1, a domain required for activation by actin, and a relatively uncharacterized N-terminal domain.

We have solved the high-resolution crystal structure of the Rho-GTPase binding domain of YpkA with its small GTPase host target Rac1. Analysis of this structure and biochemical data reveal that YpkA mimics host guanine nucleotide dissociation inhibitors, or GDIs, for the Rho family of small GTPases. This interaction with Rac1 is critical for the cytoskeletal disruption induced by YpkA in cell culture and is also crucial for virulence in mice.

 

G. Prehna, M. I. Ivanov, J.B. Bliska, and C.E. Stebbins (2006). "Yersinia Virulence Depends on Mimicry of Host Rho-family Nucleotide Dissociation Inhibitors." Cell, 126(5): 869-80.
[Abstract]  [pdf] [pdb YpkA Rho Binding Domain] [pdb YpkA-Rac1 complex]

X. Hu, G. Prehna, C.E. Stebbins. (2007) "Targeting plague virulence factors: a combined machine learning method and multiple conformational virtual screening for the discovery of Yersinia protein kinase A inhibitors."  J Med Chem. 23;50(17):3980-3. PMID: 17676727 [Abstract]  [pdf]

 

Dr. Gerd Prehna was the lead scientist on the YpkA project.  Our collaborators were the group of Dr. James Bliska at SUNY Stony Brook.