| Copper homeostasis in Escherichia coli is mediated in part by a copper sensing system (the Cus system) that includes a tripartite protein complex, CusCBA, which spans both the inner and outer membranes of E. coli. The inner membrane protein, CusA, belongs to the RND superfamily of protein transporters and couples the export of copper ions with an influx of protons. CusB, the membrane fusion protein, is a soluble protein that forms a complex with CusA and is believed to interact with CusC, the outer membrane factor protein. CusF, the fourth component of this system, is a small periplasmic metallochaperone that delivers metal to the CusCBA pump. The research presented in this work describes the elucidation of protein-protein interactions and metal transfer between components of the Cus system. Chemical cross-linking and mass spectrometry reveal that CusF and CusB interact at their metal-binding sites. The N-terminal region of CusB, which includes the metal-binding site, is characterized utilizing a variety of biochemical and molecular tools and demonstrates metal-binding and metal transfer with CusF. Cross-linking experiments and XAS preliminary results reveal a novel interaction between CusF and CusA, which supports our theory that CusA acquires metal from CusF rather than CusB. Together, these findings aid in our understanding of the mechaniam of metal transport and the molecular details involved in protein-protein interactions within CusCFBA. |
