Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

摘要

Bioinorganic canon states that active-siteudthiolate coordination promotes rapid electron transfer (ET)udto and from type 1 copper proteins. In recent work, we haveudfound that copper ET sites in proteins also can be constructedudwithout thiolate ligation (called “type zero” sites). Here weudreport multifrequency electron paramagnetic resonanceud(EPR), magnetic circular dichroism (MCD), and nuclearudmagnetic resonance (NMR) spectroscopic data together withuddensity functional theory (DFT) and spectroscopy-orientedudconfiguration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and typeudzero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centersudrelative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1udcenters. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to theudorientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding.