The role of YopN, SycN, YscB and TyeA in the regulation of virulence protein secretion and translocation via the type III secretion system of Yersinia pestis

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Gregory V. Plano, Committee Chair


Human pathogenic Yersinia resist host defenses, in part through the expression and delivery of a set of plasmid-encoded virulence proteins termed Yops. In this study we characterize products in the role of the yopN, tyeA, sycN and yscB gene the regulation of Yop secretion in Y. pestis. Mutants specifically defective in expression of YopN, TyeA, SycN or YscB were no longer able to block Yop secretion in the presence of calcium. In addition, the secretion of YopN was specifically reduced in both the sycN and yscB deletion mutants.These results indicate that a complex composed of SycN and YscB functions as a specific chaperone for YopN in Y. pestis.We also investigated the role of YopN, TyeA, SycN and YscB in the translocation of YopE into eukaryotic cells. We developed a novel reporter system designed to allow the specific identification of Yop proteins translocated into a eukaryotic cell. This reporter system is based on a bipartite phosphorylatable peptide tag, termed the Elk-tag. We demonstrate that mutants defective for the production of YopN, TyeA, SycN and YscB translocate reduced levels of Yops into eukaryotic cells. However, the reduced levels of translocated Yops in these mutants is not a direct result of the deficiency of YopN, SycN, YscB or TyeA but instead, is most likely due to a loss of the regulation of secretion associated with these mutants, and therefore, a loss in the polarized transfer of Yops directly into eukaryotic cells. In addition, we show that YopN is not translocated into host cells as has been previously speculated.We also characterized the YscX and YscY proteins which directly downstream of sycN in the yopNtyeAsycNyscXYV operon. Yersinia pestis mutants defective for production of YscX or YscY were unable to export the Yops and V antigen. YscY, like SycN and YscB, showed significant structural and amino acid sequence similarities to the Syc family of proteins. YscY specifically recognized and bound to a region of YscX that included a predicted coiled-coil region. These data suggest that YscY may function as a specific chaperone for YscX in Y. pestis. (Abstract shortened by UMI.)


Biology, Microbiology; Health Sciences, Immunology

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