Yersinia pestis YopK contributes to immune evasion and cell death to promote plague

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] YopK is a 21-kilodalton protein that is secreted and translocated by the type three secretion system of Yersinia pestis, the causative agent of pneumonic, bubonic, and septicemic plague. This protein has previously been found to control the translocation of the other effector proteins into the host cell, suggesting it had a regulatory function only. We have found that YopK is required for virulence in both a pneumonic and septicemic model of plague in a mouse. During pneumonic plague, YopK contributes to apoptosis of both alveolar and interstitial macrophages and modulates the lung environment to allow establishment of bronchopneumonia, including manipulation of inflammation involving macrophages, dendritic cells, B cells, and CCR2+ populations. These CCR2+ cells and B cells contribute to bacterial clearance and promote the resolution of inflammation during pneumonic plague. Surprisingly, YopK also aided in suppressing all populations of CCR2+ cells in the lung during early infection, suggesting the biphasic response to pneumonic plague may actually involve an early suppression of immune populations that is at least partially dependent on the presence of YopK. In a structure function analysis of the protein, YopK appears to have a structural similarity to a small GTPase and may be functioning as a GTPase mimic in the host cell to contribute to caspase-3 cleavage. This function involved two charged residues in the putative effector binding site of YopK. These data suggest that YopK is a necessary and multi-functional protein that contributes to the success of Y. pestis during plague.