Electron tunneling in proteins: coupling through a beta strand

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Science  23 Jun 1995:
Vol. 268, Issue 5218, pp. 1733-1735
DOI: 10.1126/science.7792598


Electron coupling through a beta strand has been investigated by measurement of the intramolecular electron-transfer (ET) rates in ruthenium-modified derivatives of the beta barrel blue copper protein Pseudomonas aeruginosa azurin. Surface histidines, introduced on the methionine-121 beta strand by mutagenesis, were modified with a Ru(2,2'-bipyridine)2(imidazole)2+ complex. The Cu+ to Ru3+ rate constants yielded a distance-decay constant of 1.1 per angstrom, a value close to the distance-decay constant of 1.0 per angstrom predicted for electron tunneling through an idealized beta strand. Activationless ET rate constants in combination with a tunneling-pathway analysis of the structures of azurin and cytochrome c confirm that there is a generally efficient network for coupling the internal (native) redox center to the surface of both proteins.