title: Comparison of intra- vs intermolecular long-range electron transfer in crystals of ruthenium-modified azurin.
abstract: Selective metal-ion incorporation and ligand substitution are employed to control whether electrons tunnel over intra- or intermolecular separations in crystals of P. aeruginosa azurin modified with Ru-polypyridine complexes. Cu(1+)-to-Ru3+ electron transfer (ET) across a specific protein-protein interface in the crystal lattice has a time constant 5-10 times longer than ET between the same donor and acceptor within a single protein (tauET = 5 vs 0.5-1.0 micros). Slower intermolecular ET agrees well with a longer distance between redox centers across the inter-protein (18.9 A) compared to the intra-protein separation (17.0 A) and indicates that the closest donor/acceptor pair dominates crystal ET. Lowering the crystal pH accelerates inter-protein ET (tauET = 1.0 micros) but not intra-protein ET. Faster inter-protein ET likely results from a pH-induced peptide bond flip that perturbs hydrogen bonding in the path between Ru and Cu centers on adjacent molecules.
authors.forename: Cristian
authors.initials: C
authors.lastname: Gradinaru
authors.forename: Brian R
authors.initials: BR
authors.lastname: Crane
mesh_terms: D001400:Azurin / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D003300:Copper / Q000737:chemistry*; D003460:Crystallization; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D010777:Photochemistry; D011506:Proteins / Q000737:chemistry*; D011550:Pseudomonas aeruginosa / Q000378:metabolism; D012428:Ruthenium / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D008024:Ligands; D011506:Proteins; D001400:Azurin; D003300:Copper; D012428:Ruthenium