PROSITE documentation PDOC51485

Phytocyanin domain profile

Among the blue copper proteins with a single type I (or "blue") mononuclear copper site, the plant-specific phytocyanins constitute a distinct subfamily that can be further subdivided into the families of uclacyanins, stellacyanins, plantacyanins, and early nodulins. Stellacyanins have a blue copper coordinated by two His, one Cys and one Gln. In plantacyanins and uclacyanins, the ligands of the type-I Cu sites are two His, one Cys and one Met [1,2,3,4]. Early nodulins lack amino acid residues that coordinate Cu, so they are believed to be involved in unknown processes without binding Cu [5]. Phytocyanins are found in chloropasts of higher plants.

The phytocyanin domain has a core of seven polypeptide strands arranged as a β-sandwich comprising two β-sheets, β-sheet I and β-sheet II (see <PDB:1WS8>). β-sheet I consists of three β-strands and β-sheet II consists of four β-strands. A disulfide bridge close the metal center is characteristic for phytocyanins, in contrast to azurins, pseudoazurins, and plastocyanins, where a disulfide bond is located on the distal side of the β-barrel. This disuldide bridge may play a crucial role in maintaining the tertiary structure of the protein and/or the formation of the copper binding center because one of the His ligands of copper is followed directly by a bridging Cys residue [1,2,3,,4].

Some proteins known to contain a phytocyanin domain are listed below:

• Cucumber basic protein (CBP).
• Spinach basic protein (SBP).
• Cucumber stellacyanin (CST).
• Zucchini mavicyanin.

The profile we developed covers the entire phytocyanin domain.