Master of Science
Microbiology and Immunology
Heinrichs, David E.
Staphylococcus aureus employs an arsenal of virulence factors for survival and pathogenesis, including the fibronectin binding proteins (FnBPs) which facilitate adhesion, cell invasion, and biofilm formation. Overexpression of FnBP-A in MRSA USA300 has also been shown to cause serum-, FnBP-A-, and growth dependent hyperclumping in vitro. The fnbA gene encodes the topogenic YSIRK motif associated with protein localization to the cross wall of actively growing cells. This study investigated the role of FnBP-A localization on FnBP-A-mediated phenotypes by assessing the impact of swapping the encoded signal peptide of fnbA as a means of mislocalizing the protein. Contrary to the conventional understanding of YSIRK proteins, we did not observe FnBP-A localized within the cross wall. Instead, we showed the YSIRK motif likely promotes enhanced FnBP-A secretion and expression. Understanding the mechanisms influencing virulence factor function, including topogenic motifs, enhances our understanding of S. aureus pathogenesis, informing the development of novel therapeutics.
Summary for Lay Audience
Staphylococcus aureus is a bacterium commonly acquired in hospital and community-based settings, in which it can remain harmless, colonizing the skin and nostrils of individuals. However, under certain conditions, this opportunistic pathogen can transition from a commensal state to establish any number of serious infections and potentially lethal diseases. S. aureus can infect virtually all organs, in part due to the arsenal of proteins presented on the surface of the bacteria which interact both directly and indirectly with host tissues and proteins, such as those of the extracellular matrix (ECM). These interactions are utilized by S. aureus to adhere to host cells and establish foci of infection. This study focused on the surface protein, fibronectin binding protein A (FnBP-A), involved in adherence to the ECM, host cell entry and immune evasion. Recently we observed that overexpression of FnBP-A also contributes to the formation of large bacterial aggregates, and we have linked this to increased morbidity and mortality during systemic infection of mice. Work by other research groups has linked the presentation of proteins in certain cell surface locations to specific protein characteristics. One such characteristic possessed by FnBP-A has been shown to target proteins specifically to the plane of division separating dividing cells during growth. Here we investigated how the location of FnBP-A in the division plane could influence S. aureus characteristics associated with FnBP-A, such as cell entry and bacterial clumping. We were surprised to find FnBP-A is not located within the expected location between dividing cells, instead appearing at the cell surface in punctate foci. These findings challenge our current understanding of staphylococcal protein characteristics involved in surface location targeting, contrasting the current consensus within the literature. By gaining a better understanding of how protein characteristics influence protein function we can gain critical insights into how S. aureus elicits infection and disease for exploitation in the development of new anti-staphylococcal treatments.
LeBlanc, Camille, "The Effects of Cell Envelope Localization of FnBP-A on Staphylococcus aureus FnBP-A Dependent Phenotypes" (2023). Electronic Thesis and Dissertation Repository. 9699.
Available for download on Sunday, August 31, 2025