Methylamine dehydrogenase structure

Methylamine Dehydrogenase Structure and Function of Electron Transfer Complexes... 

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. 

Figure 15-9 Stereoscopic view of the large domain (residues 1-383) of tri-methylamine dehydrogenase from a methylotrophic bacterium. The helices and 3 strands of the (aP)8 barrel are drawn in heavy lines as are the FMN (center) and the Fe4S4 iron-sulfur cluster at the lower right edge. The a/P loop to which it is bound is drawn with dashed lines. The 733-residue protein also contains two other structural domains. From Lim et al.150 Courtesy of F. S. Mathews.

Chen, L., Durley, R., Mathews, F. S., and Davidson, V. L., 1994, Structure of an electron transfer complex Methylamine dehydrogenase, amicyanin and cytochrome c-551i. Science 264 86990. 

Three-dimensional structures. The TPQ-con-taining amine oxidase from E. coU is a dimer of 727-residue subunits with one molecule of TPQ at position 402 in each subunit. 7458 Methylamine dehydrogenase is also a large dimeric protein of two large 46.7-kDa subunits and two small 15.5-kDa subunits. Each large subunit contains a TTQ cofactor Reduced TTQ is reoxidized by the 12.5-kDa blue copper protein amicyanin. Crystal structures have been determined for complexes of methylamine dehydrogenase with amicyanin and of these two proteins with a third protein, a small bacterial cytochrome... 

Galactose oxidase has a unique tertiary structure for a copper protein, comparable with that of the non-copper protein methylamine dehydrogenase. Comparisons of the amino acid sequences [157] show, however, that the enzymes are not phylogenetically related. The tertiary structures developed separately [30]. 

Figure 5 Structure of the TTQ cofactor in methylamine dehydrogenase from P. denitrificans. In this enzyme oxygenation of /3Trp57 and cross-linking with /3Trp108 yields the TTQ cofactor, which is displayed as sticks colored gray for carbon, red for oxygen, and blue for nitrogen. The coordinates from PDB entry 2bbk were used to display this structure.

These cross-linked amino acid residues appear to have no direct participation in the catalytic mechanism. They do play a structural role in determining the tertiary structure of the 7 suhunit. It is interesting to note that the TTQ dependent methylamine dehydrogenase does not have these thioether cross-linked residues, but does have six intra-subunit disulfide bonds between cysteine residues, which play a structural role in determining the tertiary structure of the TTQ bearing (3 subunit of that enzyme. The a subunit of QHNDH contains two r-type hemes. One heme c is solvent-accessible and the other is fully buried within the a subunit and located approximately 9 A from the tryptophylquinone moiety of CTQ on the 7 subunit. The a and 7 subunits sit on the surface of the / subunit that with the 7 subunit forms the enzyme active site. 

B. Structure and Function of Methylamine Dehydrogenase and Cytochrome c Oxidase... 

Fig. 15. Representation of the structure of methylamine dehydrogenase based on the crystal structure 60, 159). The secondary structure elements, j8-sheets and a-heli-ces, are indicated as plates. The cofactor TTQ is presented in a ball-and-stick form. (Top) This representation shows clearly the small and large subunits, with the extended arm of the large subunit embracing the small subunit. (Bottom) The molecule is turned 90° with respect to the orientation in the top drawing, along the sevenfold symmetry present in the large subunit. A remarkable feature is that the cofactor is located on the extension of this sevenfold axis.

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]. 

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