Cupredoxins 3-barrel structure

In summary, then, comparison of the four known cupredoxin structures helps reveal the essence" of this kind of protein. Schematically (see Fig. 6), it can be seen that the jS-barrel structure is composed of three parts an amino-terminal portion, a middle portion, and a carboxy-terminal portion (a functional grouping which probably is not relevant to the folding of the polypeptide). One part of the amino-terminal loop... 

The location of the copper with respect to the Greek key fold is interesting when compared to that of the cupredoxins. While the copper in the cupredoxins lies in the interior of the /8 barrel bound by three interior-facing residues of the carboxy-terminal loop in the )8 barrel, and by a histidine in an adjacent strand, the copper in SOD lies on the outside of its jS barrel, bound by one residue from the carhoxy-terminal loop and three from the adjacent strand (cf. Figs. 2c-5c with Fig. 8c.) A structural comparison of plastocyanin and SOD, coupled with sequence alignment of plastocyanin and ceruloplasmin (Ryden, 1988), showed that three of the SOD ligands correspond to putative copper ligands in ceruloplasmin. Why this is so will become more evident after the description of the ascorbate oxidase structure and its relationship to ceruloplasmin. 

Figure 1 Schematic illustration of overall fold (a) and topology (b) of a typical Greek key j3 barrel motif, and overall structure (c) and topology (d) of a typical cupredoxin motif, using azurin as an example.

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