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 Å, 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–O3N 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.

Methionine, tryptophan, and histidine oxidation in a model protein, PTH: Mechanisms and stabilization

“…It is possible that His oxidation depends on the presence of copper. Inclusion of imidozole favors the coordination of the copper binding and subsequently facilitates His oxidation 54. It is prudent to examine the influence of copper on the oxidation of the three His residues in PTH.…”

N–H···N Hydrogen Bonds Involving Histidine Imidazole Nitrogen Atoms: A New Structural Role for Histidine Residues in Proteins

“…Histidine is most frequently found to be a coordinating residue in metal-binding sites of many proteins. It acts as a ligand for metal ions like copper, nickel, iron, and zinc. − The imidazole ring of histidine also participates in several noncovalent interactions involving the π-electron cloud of its aromatic ring. Its basic character allows the residue to take part in salt-bridge interactions.…”

A novel function of Mycobacterium tuberculosis chaperonin paralog GroEL1 in copper homeostasis

“…It is also imperative to identify the residues involved in metal binding. EXAFS study is helpful in identifying coordination of copper binding to GroEL1 [54]. However, through our ITC study with histidine‐rich C‐terminal deletion construct of GroEL1 protein (GroEL1‐Δ18), we can say that histidine residues are involved in copper binding (loss of exothermic binding isotherm).…”