Protein function evolution dehydrogenase

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). 

A fold also can be formed by one domain. In the example of secondary structures provided by lactate dehydrogenase (see Fig. 7.8), domain 1 alone forms the nucleotide binding fold. This fold is a binding site for NAD or, in other proteins, molecules with a generally similar structure (e.g., riboflavin). However, many proteins that bind NAD or NADP contain a very different fold from a separate fold family. These two different NAD binding folds arise from different ancestral lines and have different structures, but have similar properties and function. They are believed to be the product of convergent evolution. 

EVOLUTION OF PROTEIN STRUCTURE AND FUNCTION 705 (a) Lactate dehydrogenase (ILDN.pdb), domain 1 NAOH peroxidase (lNPX.pdb), domain 4... 

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