Copper type I proteins

In the blue, Type I copper proteins plastocyanin and azurin, the active-site structure comprises the trigonal array [CuN2S] of two histidine ligands and one cysteine ligand about the copper,... 

From the standpoint of modeling Type I copper proteins,4,5,59,60 a variety of imidazole-based ligands containing thioether sulfurs and imidazole groups have been synthesized.61,62 The structures and spectroscopic properties of their copper(II) complexes (51)-(53) and (55)-(60) were investigated.65,79-82 To characterize apical copper(II)-thioether bonding, the complex (51) was... 

In their pursuit of modeling Type I copper proteins, Kitajima et al. reported112 a rare, tetrahedrally coordinated complex (105), which displayed an EPR spectrum consistent with the presence of the unpaired electron in the dz2 orbital.1 They also isolated a square-pyramidal DMF adduct (complex (106)). They were successful in providing structural proof of a copper(II) complex (trigonal pyramidal) with C6F5S -coordinated complex (107), with CuN3S chromo-phore.113 The X-ray analysis (poor data set) of a closely similar complex with Ph3CS as the... 

Model systems for Type I copper proteins structures of copper coordination compounds with thioether and azole-containing ligands.17... 

When copper is bound to one sulfur atom of a cysteine and two nitrogens of two histidines in an essentially tetrahedrally distorted - trigonal ligand environment (type I copper proteins), the excited levels are low in energy, and the values are reduced to about 5 x 10 ° s (29). Examples are blue copper proteins, like ceruloplasmin and azurin, and copper(II) substituted liver alcohol dehydrogenase (30-32). 

Copper(II) sites in proteins can be classified into three types based on their spectral properties. The blue (Type I) copper proteins are characterised by a visible absorption... 

The azurin structural gene has been cloned and expressed in large amounts in E. coli (Karlson et al., 1989). The copper site in azurin is distorted-planar with two additional weakly interacting groups in axial positions. Site directed mutagenesis has been used to exchange His-46 for Met, Cys-112 for His and Met-121 for all other amino acids, in order to study the relationship between structure and function and to determine the prerequisites for the blue copper site. The Met-121 mutant proteins were characterised by their absorption and ESR spectra (Karlson et al., 1991). At low pH, all mutants exhibit the characteristics of the blue (Type I) copper protein, indicating... 

In this complex, there are two optically active sites. Spinach plastocyanin is a type I copper protein, in which two reactive sites have been identified on its surface, at least. The electron transfer reaction occurs with significantly large stereoselectivity the ratio of the observed reaction rate constant (k /k ) is 1.6 to 2.0. The difference in the activation enthalpy, AAH a, is 3.0 kJ mol-1, and the difference in the activation entropy, AS (a-a) is 15 J mol-1 K-1. This means that the stereoselectivity arises from the entropy term. 

Fig.2. Schematic drawing of the metal coordination sites in typical Type I copper proteins (A) plastocyanin (B) rusticyanin (C) stellacyanin and (D) azurin.

D. Metal Substitution in Type I Copper Proteins 1. Co(II) Substitution... 

Amicyanin is a type I copper protein in which two histidines, one cysteine and one methionine provide the four ligands for the redox-active copper. The P. denitrificans protein is composed of 105 amino acid residues. Its primary sequence is known (Van Spanning et al., 1990) and its crystal stmcture has been determined (Durley et al., 1993 Cunane et al., 1996). 

This complex catalyzes the reaction through the Q cycle (Section 18.3.4). In the first half of the Q cycle, plastoquinol is oxidized to plastoquinone, one electron at a time. The electrons from plastoquinol flow through the Fe-S protein to convert oxidized plastocyanin into its reduced form. Plastocyanin is a small, soluble protein with a single copper ion bound by a cysteine residue, two histidine residues, and a methionine residue in a distorted tetrahedral arrangement (Figure 19.17). This geometry facilitates the interconversion between the Cu2+ and the Cu+ states and sets the reduction potential at an appropriate value relative to that of plastoquinol. Plastocyanin is intensely blue in color in its oxidized form, marking it as a member of the "blue copper protein," or type I copper protein family. 

Deeth RJ (2007) Comprehensive molecniar mechanics model for oxidized type I copper proteins active site stmctines, strain energies, and entatic bnlging. Inorg Chem 46 4492... 

This extended series of ligands and their Cu(II) complexes have been prepared as spectroscopic models (observable in visible and near-IR regions) for determining the geometries and ligand coordination of copper proteins. From their results it was possible to propose the following structures for the copper coordination and geometry in (blue) type I copper proteins and for the copper site in oxyhemocyanin (251). 

The hallmark of cupredoxins, leading to their description as blue or type I copper proteins, is the presence in their... 

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