Structure-function correlation of intramolecular electron transfer in wild type and single-site mutated azurins

Intramolecular electron transfer (ET) between the Cys3-Cys26 radical ion (RSSR-) produced pulse radiolytically and the Cu(II) ion has been studied in four wild type and nine different single site mutants of the blue single-copper protein, azurin. This enabled examination of the rate of this intramolecular ET as a function of driving force and the nature of the medium separating the electron donor and acceptor. Using a tunneling pathway model for ET from donor (RSSR(-)) to acceptor (Cu[II]) through a combination of covalent bonds, hydrogen bonds, and space (van der Waals contact) jumps, the electronic coupling decays for protein mediated ET were calculated and potential pathways operating within the different azurins could be predicted, The rates of intramolecular ET and activation parameters for the above azurins correlate well with pathway distance and driving force as predicted by the Marcus theory, using a through-bond ET mechanism.