Structure of blue copper proteins

A. The Diamagnetic Copper(I) State Spectroscopic Studies and Solution Structures of Blue Copper Proteins... 

The crystal structures of blue copper proteins show that the T1 site is in a trigonally distorted tetrahedral environment (Fig. la) [34—40]. The trigonal plane has a very short ( 2.1 A) Cu-S(Cys) and two typical ( 2.0 A) Cu-N His bonds. An additional axial thioether ligand is usually present with a long Cu-S(Met) bond ( 2.8 A), although the Met residue is replaced by a non-ligating one, such as Lys or Phe, in some tree and fungal laccases [41-44]. 

Structure is reported to be 2.5 A. This is unlikely to be a real difference, in view of the consistency of geometry seen between many kinds of blue copper proteins. 

Type II Cu(II), or low-blue copper, is less colored at common research concentrations. These systems have received less attention than Type I copper. However, even low-blue cupric copper can possess high molar absorbtivities when compared with simple coordination complexes of Cu(II). The Cu(II) sites in such proteins also yield Azz values normally greater than 140 G, i.e., more like that of low molecular weight square planar Cu(II) complexes (2, 8). The only available crystal structure of a copper protein is that of a low blue protein bovine erythrocyte superoxide dismtuase (9). The two copper atoms in this protein are each coordinated to four histidine nitrogens in an approximate square planar array. 

Gray, H. B., Solomon, E. I. Electronic structure of blue copper centers in proteins, in Copper Proteins (ed.) Spiro, T. G., chapter 1, New York, Wiley-Interscience 1981... 

A keyword search will provide access to coordinate sets from all species that are currently available as well as various site-directed mutants, type 1 copper proteins substituted with metals other than copper, and ruthenated blue copper protein derivatives. Table 1 provides a summary (with references) of the structures of blue copper-binding domains elucidated using X-ray crystallography and NMR spectroscopy. 

Some of the first protein systems where pulse radiolysis was used to help determine mechanism were those of blue copper proteins. These are proteins that are blue in solution and contain what are known as type (I) and type (2) copper centers. Two of the most well-known and well-characterized examples of these are azurin and cytochrome c. It was the studies of these systems that opened up the field of long-distance electron transfer in proteins and, by using the protein structure as a framework for electron transfer through space and through bonds, allowed for the development of a broad theoretical basis and many fascinating experiments on long-range electron transfer. Here, I will limit the discussion to electron transfer studies in azurin as illuminated by pulse radiolysis studies. ... 

Rusticyanin (Rc), a member of blue copper proteins (BCP) which are relatively small, soluble electron-transfer proteins. Rc possesses a -barrel structure and is arranged in a so-caUed Greek key topology. It shows the highest redox potential (680 mV) of the BCP family, and is particularly efficient in stabilizing the copper (I) ion [F. Nunzi et al., Biochem. Biophys. Res. Com-mun. 1994, 203, 1655 L. A. Alcaraz et al.. Protein Sci. 2005, 14,1710]. 

Blair DF, Campbell GW, Cho WK, English AM, Fry HA, Lum V, Norton KA, Schoonover JR, Chan SI. Resonance Raman studies of blue copper proteins effects of temperature and isotopic substitutions. Structural and thermodynamic implications. J Am Chem Soc 1985 107 5755-5766. 

Structure and electron transfer reactivity of the blue copper protein, plastocyanin. A. G. Sykes, Chem. Soc. Rev., 1985,14, 283 (117). 

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