Electron transfer cupredoxins

Blue (or type 1 ) copper proteins (or cupredoxins) are important components of biological electron transfer processes in many organisms ranging from bacteria to animals, from fungi to plants.56 They are characterized by ... 

It has long been known that, under some conditions at least, electron transfer between the c and d hemes of the P aeruginosa enzyme is slow and requires times of the order of seconds (22). What does this mean It is not necessarily related to the loss of the hydroxide ligand from the d heme iron, because under some experimental conditions used, azurin (a cupredoxin) was present and the enzyme was reduced at the outset,... 

The constrained nature of the copper center in BCB domains reduces its reorganization energy, which is considered an important feature for their function in long-range electron transfer processes. They are capable of tunneling electrons, usually over 10- to 12-A distances, intramolecu-larly within the same protein (in the case of multicopper oxidases and nitrite reductases) or intermolecularly between a donor and an acceptor protein (in the case of cupredoxins) in a thermodynamically favorable environment. 

With a few exceptions, cupredoxins are freely diffusible proteins. They accept and donate a single electron to their redox partners during which process the protein-bound copper oscillates between Cu(II) and Cu(I). The cupredoxin and its redox partners form a transient complex that will dissociate upon a successful electron transfer act. Therefore, the protein-protein interactions between a diffusible cupredoxin and its redox partner may not be as specific as one might expect. Indeed, the binding... 

Cupredoxins are found primarily in Bacteria and in Archaea. None have been identified in vertebrates, nematodes, insects or unicellular eukaryotes, but they do exist in plants. Where their function has been established, they act as freely diffusible electron-shuttle proteins in a variety of electron-transfer chains for energy conversion. 

Copper ions are found in electron transfer proteins such as the cupredoxins and in enzymes such as Cu-Zn superoxide dismutase. Cu has a long Xs and is thus effective... 

Electron transfer copper proteins usually belong to the blue copper proteins (Type 1) azurin is a simple example. This family of proteins are also called cupredoxins, and they participate in many redox reactions involved in processes fundamental to biology, such as respiration or photosynthesis. The striking electron transfer capabilities of blue copper proteins have been studied extensively. Plastocyanin, with a tetrahedral CUN2S2 core, acts as the electron donor to Photo System I in photosynthesis in higher plants and some algae. 

The trigonal Cu(Cys)(His)2 unit is a recurring motif in cupredoxins, more commonly known as blue copper proteins, which are principally involved in electron transfer in the high potential... 

Cupredoxins refer to a group of copper proteins that share the same overall structural fold and perform biological electron transfer (ET) through their redox reactivity. The term cupredoxin comes from ferredoxin, the Fe-containing redox proteins. Cupredoxins comprise one of the three classes of metalloproteins known to carry out biological electron transfer, after cytochromes (see Chapter 8.2) and ferredoxins (see Chapter 8.3). 

Type 1 copper proteins are the class of proteins for which cupredoxins were originally named. Type 1 copper proteins include both proteins with known electron transfer function (e.g., plastocyanin and rusticyanin), and proteins whose biological functions have not been determined conclusively (e.g., stellacyanin and plantacyanin). Although these proteins with unknown function cannot be called cupredoxins by the strict functional definition, they have been classified as cupredoxins because they share the same overall structural fold and metal-binding sites as cupredoxins. In addition, many multidomain proteins, such as laccase, ascorbate oxidase, and ceruloplasmin, contain multiple metal centers, one of which is a type 1 copper. Those cupredoxin centers are also included here. Finally, both the Cua center in cytochrome c oxidase (CcO) and nitrous oxide reductase (N2OR), and the red copper center in nitrocyanin will be discussed in this chapter because their metal centers are structurally related to the type 1 copper center and the protein domain that contains both centers share the same overall structural motif as those of cupredoxins. The Cua center also functions as an electron transfer agent. Like ferredoxins, which contain either dinuclear or tetranuclear iron-sulfur centers, cupredoxins may include either the mononuclear or the dinuclear copper center in their metal-binding sites. 

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