title: Pi-pi interaction between aromatic ring and copper-coordinated His81 imidazole regulates the blue copper active-site structure.
abstract: Noncovalent weak interactions play important roles in biological systems. In particular, such interactions in the second coordination shell of metal ions in proteins may modulate the structure and reactivity of the metal ion site in functionally significant ways. Recently, pi-pi interactions between metal ion coordinated histidine imidazoles and aromatic amino acids have been recognized as potentially important contributors to the properties of metal ion sites. In this paper we demonstrate that in pseudoazurin (a blue copper protein) the pi-pi interaction between a coordinated histidine imidazole ring and the side chains of aromatic amino acids in the second coordination sphere, significantly influences the properties of the blue copper site. Electronic absorption and electron paramagnetic resonance spectra indicate that the blue copper electronic structure is perturbed, as is the redox potential, by the introduction of a second coordination shell pi-pi interaction. We suggest that the pi-pi interaction with the metal ion coordinated histidine imidazole ring modulates the electron delocalization in the active site, and that such interactions may be functionally important in refining the reactivity of blue copper sites.
authors.affiliation: Institute of Applied Beam Science, Ibaraki University, Mito, Ibaraki, 310-8512, Japan.
authors.forename: Rehab F
authors.initials: RF
authors.lastname: Abdelhamid
authors.forename: Yuji
authors.initials: Y
authors.lastname: Obara
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Uchida
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Kohzuma
authors.forename: David M
authors.initials: DM
authors.lastname: Dooley
authors.forename: Doreen E
authors.initials: DE
authors.lastname: Brown
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hori
mesh_terms: D019943:Amino Acid Substitution; D001400:Azurin / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification; D001665:Binding Sites; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry* / Q000378:metabolism; D008667:Metalloproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D007093:Imidazoles; D008667:Metalloproteins; C047163:pseudoazurin; D001400:Azurin; D006639:Histidine; D003300:Copper; C029899:imidazole