Open AccessEnhanced rate of intramolecular electron transfer in an engineered purple Cu A azurin
Author(s) -
Ole Farver,
Yi Lu,
Majorie C. Ang,
İsrael Pecht
Publication year - 1999
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.96.3.899
Subject(s) - azurin , copper protein , electron transfer , copper , intramolecular force , chemistry , crystallography , photochemistry , stereochemistry , organic chemistry
The recent expression of an azurin mutant where the blue type 1 copper site is replaced by the purple CuA site ofParacoccus denitrificans cytochromec oxidase has yielded an optimal system for examining the unique electron mediation properties of the binuclear CuA center, because both type 1 and CuA centers are placed in the same location in the protein while all other structural elements remain the same. Long-range electron transfer is induced between the disulfide radical anion, produced pulse radiolytically, and the oxidized binuclear CuA center in the purple azurin mutant. The rate constant of this intramolecular process,k ET = 650 ± 60 s−1 at 298 K and pH 5.1, is almost 3-fold faster than for the same process in the wild-type single blue copper azurin fromPseudomonas aeruginosa (250 ± 20 s−1 ), in spite of a smaller driving force (0.69 eV for purple CuA azurin vs. 0.76 eV for blue copper azurin). The reorganization energy of the CuA center is calculated to be 0.4 eV, which is only 50% of that found for the wild-type azurin. These results represent a direct comparison of electron transfer properties of the blue and purple CuA sites in the same protein framework and provide support for the notion that the binuclear purple CuA center is a more efficient electron transfer agent than the blue single copper center because reactivity of the former involves a lower reorganization energy.