Crystallographic Study of a Quinoprotein Electron Transfer System: Methylamine Dehydrogenase

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Structural studies will be carried out on the quinoprotein-electron transfer system methylamine dehydrogenase (MADH) from Paracoccus denitrificans by the methods of x-ray diffraction. Three proteins are involved in this system, MADH, amicyanin and cytochrome c551i. MADH is a dimer of 124 kDa and contains the unusual cofactor tryptophan tryptophylquinone. Amicyanin is a blue copper protein of 12.5 kDa which interacts specifically with MADH. Cytochrome c551i is a 22 kDa protein which accepts electrons from amicyanin and transfers them via another cytochrome to a terminal oxidase. Crystals have been prepared of MADH, amicyanin, the binary complex of MADH with amicyanin and of the ternary complex of MADH, amicyanin and cytochrome c551i. The structures of MADH and the binary complex have been solved by molecular replacement to 2.8 A and 2.5 A resolution, respectively. The structures of the remaining crystal types and of the cytochrome by itself will be determined. The structures of all crystal types will be refined by simulated annealing and energy minimization. These structures will be carefully analyzed using molecular graphics to determine the catalytic mechanisms and details of the electron transfer processes.