Methylamine dehydrogenase electron amicyanin

Fig. 6. Electron transfer complex between methylamine dehydrogenase and amicyanin from Paracoccus dentrificans (PDB Accession Code 2MTA). The distance shown is between eN of the redox cofactor tryptophan tryptophylquinone of methylamine dehydrogenase and the eN of the His-95 ligand of amicyanin.

Bishop, G. R., and Davidson, V. L., 1995, Intermolecular electron transfer from substrate-reduced methylamine dehydrogenase to amicyanin is linked to proton transfer. Biochemistry 34 12082nl2086. 

Davidson, V. L., Graichen, M. E., and Jones, L. H., 1993, Binding constants for a physiologic electron-transfer protein complex between methylamine dehydrogenase and amicyanin. Effects of ionic strength and bound copper on binding, Biochim. Biophys. Acta 1144 3 9n 45. 

Aromatic residues have been found in proteins at positions that probably enhance the electronic coupling in systems that have been selected by evolution for efficient ET. Examples are the tryptophan mediated reduction of quinone in the photosynthetic reaction center (31), the methylamine dehydrogenase (MADH) amicyanin system, where a Trp residue is placed at the interface between the two proteins (32), as well as the [cytochrome c peroxidase-cytochrome c] complex, where a Trp seems to have a similar function (33). 

Pathways can yield reliable predictions of the electronic couplings, where the CT process in proteins are mediated by the interactions of a single or multiple configurations that the protein can adopt [50]. Pathways has been successfully applied to a number of CT processes in protein environment. For instance, the electron transfer between the proteins cytochrome c2 (cytc2) and the photosynthetic reaction center (RC) [152] in order to determine the protein structural dependence of this CT reaction, also, to look at the impact of structural and conformational variations on the electronic coupling between the proteins methylamine dehydrogenase and amicyanin from Paracoccus denitrificans [153]. 

The blue protein from A. faecalis strain S-6, which was isolated as a requirement for transferring electrons to a copper-containing nitrite reductase, has since been shown to have sequence homology with proteins arbitrarily designated pseudoazurin by Ambler and Tobari (1985), from Achromobacter cycloclastes and from Pseudomonas AMI. [Pseudomonas AMI also produces amicyanin, which is the recipient of electrons from methylamine dehydrogenase, (see below)]. In A. cycloclastes reduced pseudoazurin donates electrons to a copper nitrite reductase (Liu et ai, 1986), as it does in A. faecalis. Ambler and Tobari (1985)... 

Although crystals have been reported for two amicyanins (Petratos et al., 1988b Lim et al., 1986), the type 1 blue protein, which is an electron acceptor for methylamine dehydrogenase (Tobari and Harada, 1981 van Houweligen et al., 1989), neither study has yet been completed. The structure of methylamine dehydrogenase from Thiobacillus versutus (not a copper protein) has recently been reported (Vellieux et al., 1989). The amicyanin from P. denitrificans has actually been cocrystallized with methylamine dehydrogenase (F. S. Mathews, personal communication. 

Davidson, V. L., Jones, L. H., and Zhu, Z., 1998, Site-directed mutagenesis of Phe 97 of amicyanin alters the electronic coupling for interprotein electron transfer from quinol methylamine dehydrogenase. Biochemistry 37 737197377. 

Tobari, J., and Harada, Y., 1981, Amicyanin an electron acceptor of methylamine dehydrogenase, Biochim. Biophys. Res. Commun. 101 502n508. 

Amicyanin is found in methylotrophic bacteria that can use methylated amines as an energy source. The inactivation of the amicyanin gene in Paracoccus denitrificans results in complete loss of its ability to grow on methylamine, a direct indication that amicyanin is a key component of the methylamine driven electron-transfer chain. Amicyanin accepts an electron from methylamine dehydrogenase and transfers it to a c-type cytochrome (see Section 5.4.5). Currently, more than a dozen amicyanin and pseudoazurin sequences are available. 

Two amicyanins from the methylotropic bacteria Pseudomonas AMI and T. versutus have been a recent focus of attention (42, 43). Their function is to mediate electron transfer between bacterial cytochrome c and methylamine dehydrogenase in a relatively short electron transport chain. 

Amicyanins function as electron carriers in the respiratory chains of some me-thylotrophic bacteria, e.g., Thiobacillus versutus [92]. They transfer single electrons from methylamine dehydrogenase to a cytochrome c [78] which then transfers the electron to cytochrome c oxidase. Amicyanin from Pseudomonas denitrificans has a molecular mass of 11.6 kD and contains 106 amino acid residues. Amicyanin contains one /J-sheet more than the eight of plastocyanin and pseudoazurin, the result of several additional amino acids at its N-terminus [78] (Fig. 15). Like pseudoazurin, amicyanin is found exclusively in bacteria. 

TTQ is a two-electron carrier and the electron acceptor for methylamine dehydrogenase, amicyanin, is a one-electron carrier. Thus, the oxidative half-reaction of methylamine dehydrogenase must occur in two... 

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