Abstract：
Gram-negative bacteriafrequently expel toxic chemicals through tripartite efflux pumps that span both the inner and outer membranes. The three parts are the inner membrane, substrate-binding transporter (or pump); a periplasmic membrane fusion protein (or adaptor); and an outer membrane-anchored channel. The fusion protein connects the transporter to the channel within the periplasmic space. One such efflux system CusCBAis responsible for extruding biocidalCu(I) and Ag(I) ions. We previously described the crystal structures of both the inner membrane transporter CusA and the membrane fusion protein CusB of E. coli. We also determined the co-crystal structure of the CusBA adaptor-transporter efflux complex, showing that the transporter CusA, which is present as a trimer, interacts with six CusBprotomers and that the periplasmic domain of CusA is involved in these interactions. Here, we summarize the structural information of these efflux proteins, and present the accumulated evidence that this efflux system utilizes methionine residues to bind and export Cu(I) and Ag(I). Genetic and structural analyses suggest that the CusA pump is capable of picking up the metal ions from both the periplasm and cytoplasm. We propose a stepwise shuttle mechanism for this pump to export metal ions from the cell.

Biography：
Dr. Edward Yu, professor, received his Ph.D. from the University of Michigan in 1997. Prior to coming to Iowa State University, Dr. Yu was an NIH Postdoctoral Fellowship at University of California-Berkeley. He started his academic career in 2004 as assistant professor of physics and astronomy at Iowa State University. His research focuses on elucidating the structure and function of membrane proteins using x-ray crystallography. Dr. Yu is currently a professor in the both the Department of Physics and Astronomy and Department of Chemistry at ISU.