title: Outer-sphere contributions to the electronic structure of type zero copper proteins.
abstract: Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called "type zero" sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero  Pseudomonas aeruginosa  azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding.
authors.affiliation: California Institute of Technology, Pasadena, California 91125, United States. kml236@cornell.edu
authors.forename: Kyle M
authors.initials: KM
authors.lastname: Lancaster
authors.forename: María-Eugenia
authors.initials: ME
authors.lastname: Zaballa
authors.forename: Stephen
authors.initials: S
authors.lastname: Sproules
authors.forename: Mahesh
authors.initials: M
authors.lastname: Sundararajan
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer
authors.forename: John H
authors.initials: JH
authors.lastname: Richards
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Vila
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
mesh_terms: D001400:Azurin / Q000737:chemistry* / Q000378:metabolism; D003300:Copper; D004583:Electrons; D008958:Models, Molecular; D011487:Protein Conformation; D011550:Pseudomonas aeruginosa; D013057:Spectrum Analysis
chemical_list: D001400:Azurin; D003300:Copper