title: Designed azurins show lower reorganization free energies for intraprotein electron transfer.
abstract: Low reorganization free energies are necessary for fast electron transfer (ET) reactions. Hence, rational design of redox proteins with lower reorganization free energies has been a long-standing challenge, promising to yield a deeper understanding of the underlying principles of ET reactivity and to enable potential applications in different energy conversion systems. Herein we report studies of the intramolecular ET from pulse radiolytically produced disulfide radicals to Cu(II) in rationally designed azurin mutants. In these mutants, the copper coordination sphere has been fine-tuned to span a wide range of reduction potentials while leaving the metal binding site effectively undisrupted. We find that the reorganization free energies of ET within the mutants are indeed lower than that of WT azurin, increasing the intramolecular ET rate constants almost 10-fold: changes that are correlated with increased flexibility of their copper sites. Moreover, the lower reorganization free energy results in the ET rate constants reaching a maximum value at higher driving forces, as predicted by the Marcus theory.
authors.affiliation: Department of Analytic and Bioinorganic Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Farver
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Marshall
authors.forename: Scot
authors.initials: S
authors.lastname: Wherland
authors.forename: Yi
authors.initials: Y
authors.lastname: Lu
authors.forename: Israel
authors.initials: I
authors.lastname: Pecht
mesh_terms: D001400:Azurin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003300:Copper / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D015202:Protein Engineering; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism; D011675:Pulse Radiolysis; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D011994:Recombinant Proteins; D001400:Azurin; D003300:Copper
keywords: Marcus inverted region; Type 1 copper; blue copper; cupredoxin; reorganization energy