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Characterizing the secretion and function of TcfA : a unique autotransporter and virulence factor in Bordetella pertussis Doebel-Hickok, Monte

Abstract

Autotransporters (ATs) are an important family of proteins that are essential for the virulence of a variety of Gram-negative bacteria. The vast majority of ATs possess a classical right handed β-helical structure which facilitates the vectorial secretion of the protein. However, not all ATs possess this classical structure. Tracheal colonization factor (TcfA) of B. pertussis is one of only a few ATs that are predicted to be relatively unstructured or to possess a coil structure. It is not known what factors are important for the secretion of non- β-helical ATs. This study sought to characterize the secretion of TcfA which could also reveal more broadly applicable requirements for the secretion of ATs and other surface exposed proteins. This thesis characterized the secretion of TcfA both in E. coli as well as in B. pertussis. The study determined that TcfA has special secretion requirements that are not met when the protein is expressed in E. coli. The unique B. pertussis chaperone Par27 was identified as an important factor for secretion via both its disruption in B. pertussis as well as via its insertion in E. coli. However, it was also determined that there are additional factors that E. coli is lacking that are important for the secretion of TcfA. The study also sought to characterize potential virulence functions of TcfA. It is known that TcfA contributes to the pathogenesis of B. pertussis, but its specific role remains to be elucidated. This study used modeling to provide support for the theory that TcfA binds Factor H in B. pertussis. However, a factor H surface binding assay determined that TcfA is not the only factor that binds the complement regulatory protein Factor H in B. pertussis. Another uniquely structured AT, BapB, was hypothesized as the potential additional factor that binds Factor H. However, additional studies are required to determine the importance of BapB. Furthermore, the study determined that TcfA does not play a large role in the serum survival of B. pertussis. In summary, this thesis characterized the secretion and some potential virulence functions of TcfA, but it also raised many additional questions.

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