Title

Diradical intermediate within the context of tryptophan tryptophylquinone biosynthesis

Authors

Authors

E. T. Yukl; F. G. Liu; J. Krzystek; S. Shin; L. M. R. Jensen; V. L. Davidson; C. M. Wilmot;A. M. Liu

Comments

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Abbreviated Journal Title

Proc. Natl. Acad. Sci. U. S. A.

Keywords

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

Abstract

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.

Journal Title

Proceedings of the National Academy of Sciences of the United States of America

Volume

110

Issue/Number

12

Publication Date

1-1-2013

Document Type

Article

Language

English

First Page

4569

Last Page

4573

WOS Identifier

WOS:000317521600041

ISSN

0027-8424

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