Amicyanin MADH interactions

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. ... 

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

The three-dimensional structures of MADH from P. versutus and P. denitrificans have been determined in the presence and absence of amicyanin, and in the presence of amicyanin and cytochrome Cssk (57, 59-61, 92, 159). The architecture of the tetramer is best described as consisting of two a/3 catal3d ic units (Fig. 15). Each a-subunit interacts with the -subunit in the a)8 catalidic units and with the a-subunit of the other a/S catal5dic unit, but there are no interactions between the two )8-subunits of the tetramer. The large subunit consists of seven... 

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. 

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