title: Investigation of the copper binding site and the role of histidine as a ligand in riboflavin binding protein.
abstract: Riboflavin Binding Protein (RBP) binds copper in a 1:1 molar ratio, forming a distinct well-ordered type II site. The nature of this site has been examined using X-ray absorption and pulsed electron paramagnetic resonance (EPR) spectroscopies, revealing a four coordinate oxygen/nitrogen rich environment. On the basis of analysis of the Cambridge Structural Database, the average protein bound copper-ligand bond length of 1.96 A, obtained by extended x-ray absorption fine structure (EXAFS), is consistent with four coordinate Cu(I) and Cu(II) models that utilize mixed oxygen and nitrogen ligand distributions. These data suggest a Cu-O 3N coordination state for copper bound to RBP. While pulsed EPR studies including hyperfine sublevel correlation spectroscopy and electron nuclear double resonance show clear spectroscopic evidence for a histidine bound to the copper, inclusion of a histidine in the EXAFS simulation did not lead to any significant improvement in the fit.
authors.affiliation: Department of Natural Sciences, University of Michigan-Dearborn, Dearborn, Michigan 48101, USA. sheilars@umd.umich.edu
authors.forename: Sheila R
authors.initials: SR
authors.lastname: Smith
authors.forename: Krisztina Z
authors.initials: KZ
authors.lastname: Bencze
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Russ
authors.forename: Kristen
authors.initials: K
authors.lastname: Wasiukanis
authors.forename: Marilee
authors.initials: M
authors.lastname: Benore-Parsons
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Stemmler
mesh_terms: D015502:Absorptiometry, Photon; D001665:Binding Sites; D003300:Copper / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006639:Histidine / Q000378:metabolism*; D008024:Ligands; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D008024:Ligands; D026901:Membrane Transport Proteins; C019079:riboflavin-binding protein; D006639:Histidine; D003300:Copper