Diradical intermediate within the context of tryptophan tryptophylquinone biosynthesis

作者：Yukl Erik T; Liu Fange; Krzystek J; Shin Sooim; Jensen Lyndal M R; Davidson Victor L; Wilmot Carrie M^*; Liu Aimin

来源：Proceedings of the National Academy of Sciences, 2013, 110(12): 4569-4573.

DOI：10.1073/pnas.1215011110

• cofactor biosynthesis
• tryptophan radical
• heme
• posttranslational modification
• electron transfer

Despite the importance of tryptophan (Trp) radicals in biology, very few radicals have been trapped and characterized in a physiologically meaningful context. Here we demonstrate that the diheme enzyme MauG uses Trp radical chemistry to catalyze formation of a Trp-derived tryptophan tryptophylquinone cofactor on its substrate protein, premethylamine dehydrogenase. The unusual six-electron oxidation that results in tryptophan tryptophylquinone formation occurs in three discrete two-electron catalytic steps. Here the exact order of these oxidation steps in the processive six-electron biosynthetic reaction is determined, and reaction intermediates are structurally characterized. The intermediates observed in crystal structures are also verified in solution using mass spectrometry. Furthermore, an unprecedented Trp-derived diradical species on premethylamine dehydrogenase, which is an intermediate in the first two-electron step, is characterized using high-frequency and -field electron paramagnetic resonance spectroscopy and UV-visible absorbance spectroscopy. This work defines a unique mechanism for radical-mediated catalysis of a protein substrate, and has broad implications in the areas of applied biocatalysis and understanding of oxidative protein modification during oxidative stress.

• 出版日期2013-3-19