Assembly and Function of the Yersinia pestis YscKLQ Complex

Yersinia pestis, the ethological agent of plague, uses the type III secretion system (T3SS) to inject effector proteins into eukaryotic cells. Effector proteins termed Yersinia outer proteins (Yops) cause cytotoxicity in host cells and apoptosis in macrophages. The T3S apparatus is a complex injectisome composed of 21 essential Yesinia secretion (Ysc) proteins. T3S substrates are targeted for secretion by secretion signals and/or chaperone binding domains. How these substrates interact with the T3S apparatus is not known. In a recent study in Salmonella they found a “sorting platform” composed of the homologs to YscQ, YscK, and YscL in Y. pestis targets substrate/chaperone complexes to the T3S apparatus for orderly secretion. We hypothesize that a similar sorting complex exists in Y. pestis and is composed of a YscKLQ complex and possibly the YscN ATPase and interacts with the N-terminal portion of YscD to deliver substrate/chaperone complexes to the T3S apparatus for secretion. In this study, I investigate the YscKLQ complex and its interactions with the N-terminal portion of YscD and substrate/chaperone complexes. We found that the N-terminal portion of YscD interacts directly or indirectly with YscQ and YscK and that YscK interacts with the components of the sorting complex, YscQ and YscL, along with T3S substrates. Since the needle type substrate, YscF in Y. pestis, was not looked at in the Salmonella study, I decided to further investigate YscF and its two chaperones YscE and YscG. We found that the YscE/YscG chaperone is not only important for the stabilization of YscF but also for the secretion of YscF