All ETDs from UAB

Advisory Committee Chair

Hui Wu

Advisory Committee Members

William Benjamin, Jr

Michael Niederweis

Moon Nahm

Janet Yother

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Streptococcal species possess a multitude of adhesins that facilitate adherence to a wide range of substrates; this is the first step necessary for the development of disease. Streptococcus parasanguinis is a primary colonizer of the oral cavity and adheres to the tooth surface using long fimbriae, which are composed of Fap1, a serine-rich repeat glycoprotein (SRRP). SRRPs are conserved in many Gram-positive bacteria and play a role in bacterial adhesion, fimbrial formation, biofilm formation, and bacterial pathogenesis. Although SRRPs play such an important role, the exact mechanism of their biogenesis remains a mystery. For Fap1, an eleven gene cluster is required for Fap1 biogenesis. The exact function of the three glycosylation-associated proteins (Gap) within this cluster remains unknown. Mutations of gap1 or gap3 produce an immature Fap1, suggesting that these Gap proteins are involved in Fap1 biogenesis. The effect of Gap2 on Fap1 biogenesis and its function is unknown. In this study, we focused on elucidating the function of Gap2 by understanding the interactions between Gap2 and Gap1 and Gap3 and how these interactions affect Fap1 biogenesis. Gap2, like Gap1 and Gap3, is required for production and export of mature Fap1, with direct effects on fimbrial assembly and bacterial adhesion. Gap2 interacts with Gap1 and Gap3 to form a stable protein complex, in which Gap2 can bind in a reversible manner to a tightly formed Gap1/3 complex. Gap2 and Gap1 protect Gap3 from being targeted selectively by ClpE ATPase to be degraded by ClpP protease. Gap2 is protected by Gap1 from being targeted by ClpC and ClpE ATPases for degradation by ClpP protease. Deletion of clpP or clpE has no apparent effect on Fap1 biogenesis if any of the three Gap proteins are absent- indicating that all three Gap proteins play a direct role in mature Fap1 biogenesis. Our studies demonstrate that the three Gap proteins work in concert in Fap1 biogenesis and reveal a new function of Gap2. This insight will help us elucidate the molecular mechanism of the biogenesis of SRRPs and can provide us possible drug targets to alter the adhesion of pathogens and thereby prevent disease.

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