Plastocyanin three-dimensional structure

The first crystal structure information on a blue copper protein, for poplar plastocyanin in the Cu(II) state, was published in 1978 (2, 3). Since then, the Cu(I) state and related apo and Hg(II) substituted forms (5, 6), the green algal plastocyanin from Enteromorpha prolifera [Cu(II)] (7), azurin from Alcaligenes denitrificans [Cu(II) and Cu(D] (8, 9), azurin from Pseudomonas aeruginosa [Cu(II)] (10, 11), as well as pseudoazurin from Alcaligenes faecalis S-6 (12), and the cucumber basic protein, both in the Cu(II) state, have been published (13), making this one of the best-documented class of proteins. In addition, information as to three-dimensional structure in solution has been obtained from two-dimensional NMR studies on French bean and Scenedesmus obliquus plastocyanins (14,15). This review is concerned in the main with the active site chemistry. Other recent reviews are listed (16-20). 

Reduction of plastocyanin by cytochrome / would presumably involve some direct interaction between them. Cyt/will be described in detail in Chapter 35, but some relevant information on the composition and structure of Cyt / is given here to provide a perspective on the PC/Cyt / interaction. Cyt /, a subunit of the Cyt complex, is a c-type cytochrome of 33 kDa molecular mass with an in situ redox potential of -370 mV. The amino-acid composition has been determined for Cyt/from several species, that for turnip being shown in Fig. 11. Turnip Cyt/, containing 252 amino-acid residues, was crystallized and its three-dimensional structure determined in 1994 by Martinez, Huang, Szczepaniak, Cramer and Smith " at 2.3 A resolution, now refined to 1.96 A (see Chapter 35). 

After the synthesis of the plastocyanin precursor in cytoplasm, the first import signal mediates the transport of the protein into the chloroplast stroma. After this signal is removed by a protease, a second import signal mediates the transfer of the protein into the thylakoid lumen. Plastocyanin then binds a copper atom, folds into its final three-dimensional structure, and associates with the thylakoid membrane. 

Electronic difference spectra of the Hg(II)-substituted blue copper protein plastocyanin have been interpreted in terms of an unusually low energy charge transfer from a cysteine S atom to the central Hg(II) atom (188). The Hg(II)-plastocyanin affords a unique opportunity for investigating the coordination geometry via the UV spectrum since the three-dimensional structure of the Hg(II)-protein complex is known to high resolution (46), as is the structure of the native copper protein (48, 74). In plastocyanin. 

At this writing, the three-dimensional sttuctures of eight different naturally occurring type 1 copper proteins are known. These include the cupredoxins plastocyanin at 1.33 A resolution (pdb code 1 PTC), azurin at 1.8 A (pdb code 2AZA), pseudoazurin at 1.55 A (pdb code IPAZ), amicyanin at 1.3 A (pdb code lAAC), auracyanin at 1.55 A (pdb code IQHQ), rusticyanin at 1.9 A (pdb code IRCY), and the phytocyanins cucumber basic protein at 1.8 A (pdb code2CBP), and stellacyanin at 1.6 A (pdb code IJER) Atomic coordinates for these and all other single-domain type 1 copper proteins are available from the Research Collaboratory for Structural Bioinformatics (RCSB) Protein Data Bank (PDB) and can be accessed online at www.rcsb.org/pdb/. 

The three-dimensional structme of plastocyanin was among the first metalloenzyme structures to be solved. Prior to this, there had been much specu-... 

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