Diradical intermediate within the context of tryptophan tryptophylquinone biosynthesis
Abbreviated Journal Title
Proc. Natl. Acad. Sci. U. S. A.
cofactor biosynthesis; tryptophan radical; heme; posttranslational; modification; electron transfer; ELECTRON-PARAMAGNETIC-RESONANCE; METHYLAMINE DEHYDROGENASE; RIBONUCLEOTIDE REDUCTASE; RADICALS; MAUG; EPR; SPECTROSCOPY; PEROXIDASE; BIOGENESIS; MECHANISM; Multidisciplinary Sciences
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.
Proceedings of the National Academy of Sciences of the United States of America
"Diradical intermediate within the context of tryptophan tryptophylquinone biosynthesis" (2013). Faculty Bibliography 2010s. 4914.