Observation of an intermediate tryptophanyl radical in W306F mutant DNA photolyase from Escherichia coli supports electron hopping along the triple tryptophan chain

摘要

DNA photolyases repair UV-induced cyclobutane pyrimidine dimers in DNA by photoinduced electron transfer. The redox-ac-tive cofactor is FAD in its doubly reduced state FADH-. Typically, during enzyme purification, the flavin is oxidized to its singly reduced semiquinone state FADH°. The catalytically potent staternFADH" can be reestablished by so-called photoactivation. Upon photoexcitation, the FADH° is reduced by an intrinsic amino acid, the tryptophan W306 in Escherichia coli photolyase, which is 15 A distant. Initially, it has been believed that the electron passes directly from W306 to excited FADH°, in line with a report that replacement of W306 with redox-inactive phenylalanine (W306F mutant) suppressed the electron transfer to the flavin [Li, Y. F.; et al. (1991) Biochemistry 30, 6322-6329].