Long-Range Electron Transfer Reactions between Hemes of MauG and Different Forms of Tryptophan Tryptophylquinone of Methylamine Dehydrogenase
详细信息 查看全文
- 作者：Sooim Shin ; Nafez Abu Tarboush ; Victor L. Davidson
- 刊名：Biochemistry
- 出版年：2010
- 出版时间：July 13, 2010
- 年：2010
- 卷：49
- 期：27
- 页码：5810-5816
- 全文大小：833K
- 年卷期：v.49,no.27(July 13, 2010)
- ISSN：1520-4995
文摘
The diheme enzyme MauG catalyzes the post-translational modification of a precursor protein of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. This six-electron oxidation of preMADH requires long-range electron transfer (ET) as the structure of the MauG−preMADH complex reveals that the shortest distance between the modified residues of preMADH and the nearest heme of MauG is 14.0 Å [Jensen, L. M. R., Sanishvili, R., Davidson, V. L., and Wilmot, C. M. (2010) Science 327, 1392−1394]. The kinetics of two ET reactions between MADH and MauG have been analyzed. Interprotein ET from quinol MADH to the high-valent bis-Fe(IV) form of MauG exhibits a Kd of 11.2 μM and a rate constant of 20 s−1. ET from diferrous MauG to oxidized TTQ of MADH exhibits a Kd of 10.1 μM and a rate constant of 0.07 s−1. These similar Kd values are much greater than that for the MauG−preMADH complex, indicating that the extent of TTQ maturity rather than its redox state influences complex formation. The difference in rate constants is consistent with a larger driving force for the faster reaction. Analysis of the structure of the MauG−preMADH complex in the context of ET theory and these results suggests that direct electron tunneling between the residues that form TTQ and the five-coordinate oxygen-binding heme is not possible, and that ET requires electron hopping via the six-coordinate heme.