Axial ligation in electron-transfer copper sites: a paramagnetic 1H NMR study.

DE CANDIA, ARIEL G.; TOMATIS, PABLO E.; PIERATTELLI, ROBERTA; RICHARDS, JOHN H.; FERNÁNDEZ, CLAUDIO O.; GRAY, HARRY B.; AND VILA, ALEJANDRO J.

Bariloche. Rio Negro. Argentina

Congreso; XXXII Reunión Anual de la Sociedad Argentina de Biofísica; 2003

Sociedad Argentina de Biofísica

Copper proteins are involved in electron transfer processes by using the mononuclear blue copper and the binuclear CuA centers. Previous studies on blue copper and CuA sites have revealed that metal-axial ligand interactions strongly affect the electronic structure of these centers.To probe the effect of various axial ligands on the spectroscopic properties of these copper sites, we have applied paramagnetic NMR spectroscopy to two variants of P. aeruginosa azurin, Met121Leu and Met121Asp, and to four mutants from the CuA– containing soluble fragment of T. thermophilus cytochrome oxidase: Met160Asn, Met160Glu, Met160Gly and Met160Gln. In the azurin mutants, a stronger interaction with the axial ligand results in a diminished electron delocalization onto the Cu-S(Cys) bond. In contrast, in the structurally more robust CuA center, the interaction with the axial ligand does not weaken the Cu-S(Cys) bond. Instead, the mutations shift the energy of a low lying electronic state. In addition, the axial ligand mutations in the CuA center induce subtle changes restricted to one half of the binuclear unit. This fact strongly supports the suggestion that axial ligand interactions determine the His orientation, and highlights the structural robustness of CuA sites, naturally exploited to provide a more efficient electron transfer machinery than blue copper centers.