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A Family of Structurally Related Secreted Proteins of Staphylococcus aureus
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The opportunistic pathogen, Staphylococcus aureus (S. aureus) can create a number of infections. The bacterium can assemble a two-layered structure composed of fibrinogen (Fg)/fibrin around itself, called the Fg shield to protect itself from being phagocytized by the immune response cells. The S. aureus proteins, Coagulase (Coa), Extracellular fibrinogenbinding protein (Efb) and von Willebrand factor-binding protein (vWbp) contribute to shield formation. Efb can contribute by binding to both soluble Fg and the complement component C3b that is deposited on the bacterial surface. The two coagulases, Coa and vWbp, can bind Fg and coagulate plasma and blood by non-proteolytically activating the coagulation factor, prothrombin that cleaves Fg to fibrin, which can contribute to the formation of the Fg/fibrin layers of the shield. The Fg interactions between Coa and Efb have been characterized to some detail. Coa and vWbp often appear to be redundant in function. However, the mechanism(s) of the interaction between vWbp and Fg appears to be unclear. In this study, I show that vWbp and Coa do not interact with Fg in the same way. Coa shows a conformation preference in binding to soluble Fg, whereas, vWbp demonstrates no preference for binding to either soluble or immobilized Fg. Both the N- and C-terminal halves of vWbp and Coa (vWbp-N, -C; Coa-N, -C, respectively) harbor Fg-binding activities. The Fgbinding activity of Coa lies in the C-terminal region, whereas, vWbp-N harbors the higher affinity Fg-binding region. vWbp and Coa do not share the same binding sites on Fg. The Nterminal regions of both coagulases interact with the Fg β-chain, but they bind to different sites. Coa-N also appears to recognize the Fg α-chain. Both the Fg-binding motifs of Coa-C and the Nterminal region of Efb do not inhibit vWbp-C from binding to Fg, indicating that vWbp-C does not harbor a similar motif. The predicted structure of vWbp-C appears to be structurally related to the C3b-binding motif of Efb. My data shows that the Fg interactions of vWbp and Coa are different and complex, and from this, it appears that S. aureus expresses a family of structurally related secreted proteins.
Thomas, Sheila Esther (2019). A Family of Structurally Related Secreted Proteins of Staphylococcus aureus. Doctoral dissertation, Texas A&M University. Available electronically from