Amicyanin protein complex

A binary complex of MADH and amicyanin (Chen et al., 1992) and a ternary protein complex of these proteins plus cytochrome c-551i (Chen et al., 1994) from P. denitrificans have been crystallized and their structures have been determined. The structures of the crystallized complexes of these proteins indicate that the interface between MADH and amicyanin is... 

Unlike the MADH-amicyanin protein interface which was discussed earlier, the amicyanin-cytochrome c-551i interface revealed in the crystal structure of the complex is relatively hydrophilic. The association between proteins appears to be stabilized by several hydrogen bond and ionic interactions (Chen et al., 1994). The shortest gap between the proteins, for consideration of a possible site for interprotein electron transfer, is from the backbone O of Glu of amicyanin to the backbone N of Glyof cytochrome c-551i, a distance of less than 3. ... 

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. 

Several copper enzymes will be discussed in detail in subsequent sections of this chapter. Information about major classes of copper enzymes, most of which will not be discussed, is collected in Table 5.1 as adapted from Chapter 14 of reference 49. Table 1 of reference 4 describes additional copper proteins such as the blue copper electron transfer proteins stellacyanin, amicyanin, auracyanin, rusticyanin, and so on. Nitrite reductase contains both normal and blue copper enzymes and facilitates the important biological reaction NO) — NO. Solomon s Chemical Reviews article4 contains extensive information on ligand field theory in relation to ground-state electronic properties of copper complexes and the application of... 

A complex of these proteins has been crystallized as a hetero-octamer comprised of one MADH tetramer, two amicyanins and two cytochromes (Chen et al., 1994). The direct distances between redox centers are 9.4 from TTQ to copper, and 23 from copper to heme (Figure 6). 

FIGURE 6. Orientation of redox cofactors in the MADH-amicyanin-cytochrome c-551i complex. A portion of the crystal structure is shown with the direct distances between the cofactors indicated. Coordinates are available in the Brookhaven Protein Data Bank, entry 2MTA. 

Phe stabilizes the MADH-amicyanin complex via van der Waalsi interactions at the protein-protein interface (see Figure 5). An F97E... 

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... 

Binding of a paramagnetic, redox-inactive [Cr(CN)6]3- anion to specific sites of a blue copper protein, amicyanin, has been used in NMR-spectroscopic studies of the protein structure in solutions.285Ab initio calculations of the ligand-field spectra of [Cr(CN)6]3 have been performed and the results compared with those for cyano complexes of the other first-row transition metals.286 The role of Cr—C—N bending vibrations in the phosphorescence spectra... 

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). 

The availability of the crystal structure of the binary complex of these two proteins (92) adds to the impact of these studies, and provides a model to which current electron transfer theories can be applied. The theoretical results can then be compared with kinetic studies of electron transfer within the complex. Additional studies 185, 186) have focused on the electron transfer reaction between MADH, amicyanin, and c5rtochrome Cssu from P. denitrificans (as pointed out in Section II, MADH and amicyanin are induced by growth on methylamine, and cytochrome Cm is induced by growth on methanol). Again, a crystal structure is available for the complex of... 

Before reviewing the details of the reactions between proteins from P. denitrificans it is important to first discuss the available structural information. The proteins MADH and amicyanin are known to associate quite strongly in solution (288). A binary complex has been crystallized and the structure (92) of part of the interface between the two proteins is shown in Fig. 20. The hydrophobic patch of amicyanin, which surrounds the exposed imidazole ring of the ligand His-96, is found associating with a mainly hydrophobic region on the L subunit of MADH. There are also interactions between amicyanin and the larger H subunit of MADH. The two proteins interact in such a way that the TTQ cofactor of MADH and the copper of amicyanin are approximately 9 A apart. 

A crystal structure is also available for a ternary complex of MADH, amicyanin, and cytochrome C55U (89, 90). The latter protein... 

Fig. 20. Position of the TTQ cofactor of MADH and the copper of amicyanin in the crystal structure of the binary complex of the two proteins. The distance from the edge of the TTQ cofactor to the Cu atom is 9.3 A. The side chain of His-96 is positioned between the Cu and the TTQ. The interface between the two proteins in the complex is formed by the hydrophobic patch of amicyanin and a similar hydrophobic surface of MADH, surrounding the exposed edge of the TTQ cofactor.

Lockwood and colleagues performed an analysis of decoherence in a ruthenium-modified blue copper protein similar to amicyanin. They found a short characteristic decoherence time of 2.4 fs, which they attributed on one hand to the diverging motion of the protein nuclei and on the other hand to the solvent molecules. Their conclusion was that both solvent and protein dynamics can affect both the rate and mechanism of electron transfer which is different to our conclusions on solvated TTQ where the solvent does not seem to play any role in decoherence. More precisely, solvent molecules start to play a role once decoherence has already occurred due to the intramolecular motions within the TTQ. Lockwood et al. used a classical force field for all the atoms, including those of the copper and ruthenium complexes, and a rigid SPC water model. In addition they did not carry out large ensembles of diverging... 

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