Phycocyanin α-Subunit Phycocyanobilin Lyase

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 15; pp. 7017 - 7021
• Main Authors: Fairchild, Craig D., Zhao, Jindong, Zhou, Jianhui, Colson, Sue Ellen, Bryant, Donald A., Glazer, Alexander N.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01-08-1992; National Acad Sciences
• Subjects: Adducts; Analytical, structural and metabolic biochemistry; attachment; Bile pigments; Bile Pigments - metabolism; bilin; Biological and medical sciences; Centrifugation; Chemical suspensions; cpcE gene; cpcF gene; Cyanobacteria - enzymology; Cyanobacteria - genetics; Cyanophyta; Enzymes and enzyme inhibitors; Fluorescence; Fundamental and applied biological sciences. Psychology; genes; Isomers; Kinetics; Lyases; Lyases - genetics; Lyases - metabolism; Macromolecular Substances; Marine; photosynthetic pigments; phycocyanin; Phycocyanin - genetics; Phycocyanin - metabolism; phycocyanobilin lyase; Plasmids; Protein precursors; proteins; Recombinant Proteins - metabolism; Resins; Restriction Mapping; sites; Spectrometry, Fluorescence; Synechococcus; Phycocyanin; Enzyme; Synechococcus; Biosynthesis; In vitro; Enzymatic activity; Cyanobacteria; Pigment protein complex; Molecular association; Bacteria; Alpha-Peptide chain; Biliprotein; Chromophore
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.15.7017

Phycobiliproteins, unlike other light-harvesting proteins involved in photosynthesis, bear covalently attached chromophores. The bilin chromophores are attached through thioether bonds to cysteine residues. The cyanobacterium Synechococcus sp. PCC 7002 has eight distinct bilin attachment sites on seven polypeptides, all of which carry the same chromophore, phycocyanobilin. When two genes in the phycocyanin operon of this organism, cpcE and cpcF, are inactivated by insertion, together or separately, the surprising result is elimination of correct bilin attachment at only one site, that on the α subunit of phycocyanin. We have overproduced CpcE and CpcF in Escherichia coli. In vitro, these proteins catalyze the attachment of phycocyanobilin to the α subunit of apophycocyanin at the appropriate site, α-Cys-84, to form the correct adduct. CpcE and CpcF also efficiently catalyze the reverse reaction, in which the bilin from holo-α subunit is transferred either to the apo-α subunit of the same C-phycocyanin or to the apo-α subunit of a heterologous C-phycocyanin. The forward and reverse reactions each require both CpcE and CpcF and are specific for the α-Cys-84 position. Phycocyanobilin is the immediate precursor of the protein-bound bilin.