Structure-function analysis of Yersinia pestis YopM's interaction with alpha-thrombin to rule on its significance in systemic plague and to model YopM's mechanism of binding host proteins

The plague virulence protein YopM of Yersinia pestis KIM5 belongs to the la rge family of leucine-rich repeat (LRR) proteins. The only activity demonst rated so far for YopM is thrombin-binding, which could be a function of the small amount of YopM that is released into surrounding tissues by the bact eria. This study combined deletional and mutational analysis, chemical cros slinking assays, and in vitro functional tests with molecular modelling to identify key features of YopM necessary for interacting with thrombin. Two Y. pestis strains expressing YopM variants that differed in thrombin bindin g were used to assess the importance of thrombin-binding for lethality of p lague. Both strains suffered a similar decrease in virulence by three order s of magnitude, indicating that thrombin-binding per se was not the major d eficiency for lethality in the systemic disease model employed. It remains possible that extracellular YopM could contribute to plague pathology and t o early events in peripheral tissues. The structural studies provided a mod el for how YopM may interact with thrombin and an insight into how YopM's L RR structure may assemble distinct regions for binding different targets. ( C) 2001 Academic Press.