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 large family of leucine-rich repeat (LRR) proteins. The only activity demonstrated 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 bacteria. This study combined deletional and mutational analysis, chemical crosslinking 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 binding were used to assess the importance of thrombin-binding for lethality of plague. Both strains suffered a similar decrease in virulence by three orders of magnitude, indicating that thrombin-binding per se was not the major deficiency for lethality in the systemic disease model employed. It remains possible that extracellular YopM could contribute to plague pathology and to early events in peripheral tissues. The structural studies provided a model for how YopM may interact with thrombin and an insight into how YopM's LRR structure may assemble distinct regions for binding different targets.