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PubMed1992

Yersinia pestis YopM: thrombin binding and overexpression.

In previous studies, Yersinia pestis YopM has been shown through mutational analysis to be necessary for virulence in mice and found to have homology with the thrombin-binding domain of the platelet receptor GPIb alpha. In this study, YopM was purified and shown by dot blot and chemical cross-linking tests to bind to human alpha-thrombin. No cross-linked product could be detected when human prothrombin was incubated with YopM. As a functional test of thrombin binding, it was shown that native but not boiled YopM inhibits thrombin-induced aggregation of human platelets. Control tests showed that YopM did not inactivate the platelets themselves, nor was its effect a nonspecific consequence of its very acidic isoelectric point. Microsequencing of YopM revealed an intact N terminus, indicating that functional YopM is not processed at the N terminus or secreted by a mechanism involving a cleavable signal sequence. Further characterization was made of an interesting effect on yopM expression that had been noticed in a previous study. A 1.5-kb HaeIII subclone overexpressed YopM in both Y. pestis and Escherichia coli compared with a larger clone containing the 5.3-kb HindIII-F fragment. To search for a possible regulator of YopM expression, the HindIII-F fragment was sequenced, revealing several open reading frames and three large repeated sequences. Deletional analysis showed that these were not involved in regulation of yopM. The data implicated a DNA structure 5' to yopM in moderating yopM expression.

Amino Acid Sequence↗

PubMed1990

YopM inhibits platelet aggregation and is necessary for virulence of Yersinia pestis in mice.

In Yersinia pestis KIM there are 11 Yops (yersinial outer membrane proteins) encoded by the low-Ca2+ response virulence plasmid pCD1. Only YopM and YopN are found in easily detectable amounts in the culture medium. In our previous work, we characterized the yopM gene. In the present study, we constructed a YopM- mutant to elucidate the role of YopM in the virulence of Y. pestis. A lacZYA sequence was inserted 126 base pairs downstream from the start codon of the yopM gene in pCD1. The YopM- mutant had the same growth properties as the parent, Y. pestis KIM5-3001. The inserted lacZ gene was regulated by the promoter of the yopM gene. Accordingly, it was expressed strongly at 37 degrees C in the absence of Ca2+ and was decreased in expression when Ca2+ was present. Northern blot (RNA blot) analysis revealed that the yopM gene was in a monocistronic operon, suggesting that the yopM insertion mutation was unlikely to have polar effects on other genes. The YopM- mutant had strongly decreased virulence in mice, with a 50% lethal dose of 3.4 x 10(5) CFU. Virulence was restored by the cloned yopM-containing 5.5-kilobase HindIII F fragment of pCD1. However, supplying a cloned 1.57-kilobase fragment containing little more than the yopM structural gene caused the yopM mutant to significantly overexpress YopM and failed to restore virulence. The infection kinetics of the YopM- mutant revealed growth in both spleens and livers from days 2 to 4 after infection, followed by a precipitous clearance of the bacteria. YopM-containing supernatant proteins of Y. pestis inhibited thrombin- or ristocetin-induced platelet aggregation, whereas there was no inhibition by supernatant proteins from the YopM- Y. pestis mutant. Accordingly, YopM may prevent platelet-mediated events and serve as an important strategy for the yersiniae in the initial stages of a plague infection.

Animals↗