A structural basis for long-range coupling in azurins from resonance Ramanspectroscopy

Resonance Raman spectra have been measured within the S --> Cu charge-trans fer band for azurins from Alcaligenes denitrificans, Pseudomonas aeruginosa , and Alcaligenes xylosoxidans. The spectra have similar frequencies but sh ow significantly different intensity patterns. Comparison of the difference s in structure and environment from the known X-ray crystal structures with resonance Raman spectral changes demonstrates a rough correlation with the overall protein structure. However, a much better correlation exists betwe en the observed resonance Raman spectral changes and specific amino acid di fferences. Comparison of the resonance Raman spectra and amino acids within 12 Angstrom of the copper site suggests that the protein-copper site coupl ing extends to at least 10 Angstrom from the copper. This experimentally ob servable, long-range coupling with specific amino acids may suggest a new m echanism for the efficient long-range electron transfer seen in these prote ins.