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Oral Biology Program
B.D.S. 1999, Beijing Medical University
Thesis Advisor: Daniel H. Fine, DMD
Department of Oral Biology
Monday, April 28, 2014
1:00 P.M., MSB C600
ApiA is an outer membrane autotransporter protein in Aggregatibacter actinomycetemcomitans (A.a), which is a gram negative bacterium causing a particular form of periodontal disease, termed localized aggressive periodontitis (LAP). Attachment is the first and essential step during the process of A.a infection. Attachment is related to the function of surface components, such as Aae, ApiA and EmaA, pili, fimbriae, and extracellular polysaccharides (PGA).
Among these proteins, ApiA is a versatile virulence factor and its various functions include binding, invasion, serum resistance, autoaggregation and inducer of cytokine release. It has been demonstrated that ApiA plays a key role in the species-specific attachment of A.a to buccal epithelial cells (BECs) from human and old world primate animals, which is the first and essential step of an A.a infection. A.a mutant strains with a double knockout of apiA and aae genes (another autotransporter protein) can not bind to BECs. Moreover, compared with the conventional autotransporter protein Aae, ApiA is a trimeric autotransporter protein, which forms a threefold symmetric structure. Taken together, ApiA could be a promising therapeutic target to inhibit A.a infection. The purpose of this project is to define the different functional domains of ApiA by mapping the apiA gene structure. The finding would be helpful in future studies designed to elucidate how ApiA contributes to A.a pathogenesis.
In this study, E.coli was used as vector for mutagenesis studies. A hybrid protein expressing ApiA and Aae was constructed to define its binding domain and to confirm the function of C-terminal region of ApiA. Since the most important function of ApiA mediates A.a binding to BECs, our goal was to define the binding domain.
The results demonstrated that the C-terminus of ApiA forms a separate domain that is crucial for general stability, autoaggregation, trimeric formation, biofilm formation and surface expression. These functions are correlated and overlapped. Importantly, results show the binding domain is located on the surface expressed N-terminus of the ApiA passenger domain, mainly from 35 a.a. to 100 a.a.