title: Models for the Metal Transfer Complex of the N-Terminal Region of CusB and CusF.
abstract: The tripartite CusCFBA pump in Escherichia coli is a very effective heavy metal extrusion system specific for Cu(I) and Ag(I). The N-terminal region of the membrane fusion protein CusB (CusB-NT) is highly disordered, and hence, experimentally characterizing its structure is challenging. In a previous study, this disorder was confirmed with molecular dynamics simulations, although some key structural elements were determined. It was experimentally shown that CusB-NT is fully functional in transferring the metal from the metallochaperone CusF. In this study, we docked these two entities together and formed two representative metal coordination modes, which consist of residues from both proteins. In this way, we created two potential CusB-NT/CusF complexes that share coordination of Cu(I) and thereby represent structural models for the metal transfer process. Each model complex was simulated for 4 μs. The previously observed structural disorder in CusB-NT disappeared upon complexation with CusF. The only differences between the two models occurred in the M21-M36 loop region of CusB-NT and the open flap of CusF: we observed the model with two CusB-NT methionine residues and a CusF methionine as the metal coordination site (termed "MMM") to be more stable than the model with a CusB-NT methionine, a CusF methionine, and a CusF histidine ligating the metal (termed "MMH"). The observed stability of the MMM model was probed for an additional 2 μs, yielding a total simulation time of 6 μs. We hypothesize that both MMM and MMH configurations might take part in the metal exchange process in which the MMH configuration would appear first and would be followed by the MMM configuration. Given the experimental finding of comparable binding affinities of CusB-NT and CusF, the increased stability of the MMM configuration might be a determinant for the transfer from CusF to CusB-NT. The metal would be transferred from the more CusF-dominated metal binding environment (MMH model) to a more CusB-dominated one (MMM model) in which the coordination environment is more stable. From the MMM model, the metal ion would ultimately be coordinated by the CusB methionines only, which would complete the Cu(I) transfer process.
authors.affiliation: †Department of Chemistry and Quantum Theory Project, University of Florida, 2328 New Physics Building, P.O. Box 118435, Gainesville, Florida 32611-8435, United States.|‡Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801-3364, United States.
authors.forename: Melek N
authors.initials: MN
authors.lastname: Ucisik
authors.affiliation: §Department of Chemistry, University of New Orleans, 2000 Lake Shore Drive, New Orleans, Louisiana 70148, United States.
authors.forename: Dhruva K
authors.initials: DK
authors.lastname: Chakravorty
authors.affiliation: ∥Institute for Cyber Enabled Research, Department of Chemistry, and Department of Biochemistry and Molecular Biology, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824-1322, United States.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Merz
mesh_terms: D027682:Cation Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D000079922:Copper Transport Proteins; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D062105:Molecular Docking Simulation; D011487:Protein Conformation
chemical_list: D027682:Cation Transport Proteins; D000079922:Copper Transport Proteins; C556452:CusB protein, E coli; C506213:CusF protein, E coli; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D003300:Copper