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MauG is a di-heme enzyme required for methylamine dehydrogenase maturation.MauG-dependent tryptophan tryptophylquinone(TTQ)biosynthesis processes need transport six electrons in a long distance,which is a typical long-range electron transfer(ET)reaction in proteins.What factors can regulate the rate of electron transfer and which pathway is the most efficient between the two hemes in MauG? In this study,we find that several amino acids between the two hemes in MauG,including His280,Phe264 and Trp93,may play vital roles in regulating electron transfer basing on the structure of the MauG-preMADH complex.The ab initio calculations reveal that these three amino acid residues may participate in electron-transfer process through a multi-step hopping mechanism.The side chains of His280 and Phe264 can form a π∴π three-electron bond to facilitate this long-range electron transfer reactions(Figure 1).In addition,further electron state analyses reveal the carboxyl groups of porphyrin rings and the side chains of cysteines can also modulate electron transfer this process.These findings may be invaluable for further understanding how the MauG-preMADH complex regulates the possible micro-structures to construct effective electron transfer channels.