Nitrite reductase evolution

The copper-containing nitrite reductase from A. cycloclastes may also have evolved from this ancestral oxidase. Nitrite reductase is a two-domain protein that functions as a trimeric molecule. During its evolution from the ancestral copper oxidase, a gene inversion must have occurred, so that domain 2 of the ancestral oxidase is now domain 1 of nitrite reductase. Domain 1 of the ancestral oxidase lost its type-1 copper but has become domain 2 in nitrite reductase after the gene inversion. 

Intramolecular ET between distinct copper centers is part of the catalytic cycles of many copper-containing redox enzymes, such as the multicopper oxidases, ascorbate oxidase, and ceruloplasmin, as well as the copper-containing nitrite reductases. Examination of internal LRET in these proteins is of considerable interest as it may also provide insights into the evolution of selected ET pathways in particular, whether and how the enzymes have evolved in order to optimize catalytic functions. With the increase in the number of known high-resolution 3D structures of transition metal containing redox enzymes, studies of structure-reactivity relationships have become feasible and indeed many have been carried out during the last two decades. 

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