Plastocyanin Cu(II) form.

Plastocyanin, also called blue copper protein, is a copper-containing protein involved in electron-transfer:
http://en.wikipedia.org/wiki/Plastocyanin

The model is of the Cu II form of plastocyanin, with four ligands to the copper (II) ion. These are N(His37) S(Cys84) N(His87) and S(Met92).

Model of Plastocyanin from Poplar based on the Protein Data Bank entry 1PLC:
http://www.rcsb.org/pdb/explore/explore.do?structureId=1plc

STL file created using VMD:
http://www.ks.uiuc.edu/Research/vmd/

The protein backbone is represented in "cartoon" form. The copper-binding histidines, cysteine and methionine, and copper ion are shown.