Long-range electron transfer reactions between hemes of MauG and different forms of tryptophan tryptophylquinone of methylamine dehydrogenase.
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 A [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 K(d) of 11.2 microM and a rate constant of 20 s(-1). ET from diferrous MauG to oxidized TTQ of MADH exhibits a K(d) of 10.1 microM and a rate constant of 0.07 s(-1). These similar K(d) 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.
Shin
Sooim
S
Department of Biochemistry, The University of Mississippi Medical Center, Jackson, Mississippi 39216-4505, USA.
Abu Tarboush
Nafez
N
Davidson
Victor L
VL
D002384:Catalysis; D004579:Electron Transport / Q000235:genetics; D004583:Electrons; D006418:Heme / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D045563:Indolequinones; D007700:Kinetics; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010100:Oxygen / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014364:Tryptophan / Q000031:analogs & derivatives
D045563:Indolequinones; C070569:tryptophan tryptophylquinone; D006418:Heme; D014364:Tryptophan; C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010100:Oxygen