Research Interests

Role of TolC in Antibiotic Efflux and Colicin Import. Harmful agents such as toxins and antibiotics present in nature, constantly challenge bacterial survival. In response to these challenges, bacterial cells have developed strategies that allow them to survive in the hostile environments in which they live. TolC is the key outer membrane protein involved in the expelling of antibiotics from inside the bacterial cell. However, TolC does not carry out such an efflux function alone; it interacts with proteins present in the inner membrane to establish a functional efflux conduit. Curiously, while helping bacteria to survive the antibiotic assault, it has been exploited by a bacterial toxin, colicin E1, to gain entry into the cell and kill bacteria that do not secrete this toxin. The involvement of TolC in secreting virulence factors makes it an important protein in bacterial pathogenesis. Studies are being conducted to (1) dissect the role of TolC residues in antibiotic efflux and colicin import, and (2) reveal various protein-protein interactions that must occur to achieve these transport activities.

Assembly of Outer Membrane Proteins in E. coli. Another research interest in our laboratory reflects the fundamental biological event of protein targeting and assembly. All proteins must reach their pre-determined cellular locations in a correctly folded conformation in order to be functionally active. We are studying how E. coli outer membrane proteins reach their destination. The uniquely structured and multifunctional TolC protein as well as OmpF and LamB, the channel-forming b-barrel porins, have been used as models. In particular, we are interested in (1) elucidating the “signal” for outer membrane targeting, (2) identifying and characterizing assembly intermediates, (3) studying the involvement of periplasmic proteins that catalyze protein folding and degradation, and (4) examining the role of lipids in the targeting and assembly of outer membrane proteins.

Bacteriophage analysis. For decades bacteriophages have been used as biological tools to study various molecular and cellular processes such as gene regulation and host-parasite interactions. Through our work on TolC, we discovered that TolC and lipopolysaccharide, an exclusively outer membrane component, are exploited as cell surface receptors by a virulent bacteriophage TLS. We are interested in studying TLS-TolC interactions as they pertain to the biology of phage infection. In order to gain a better understanding of the roles of the TLS proteins necessary for receptor binding and infection, we have been conducting both electron microscopic and genome sequence analyses. The recently completed TLS genome sequence analysis done in our laboratory revealed various novel features besides giving us an insight into the ORFs whose products might play an important role in host-parasite interactions.

These research projects are supported by NIH-R01-GM066988 and NIH-R01-GM48167 as well as several local and university grants.