Phytochrome assembly. The structure and biological activity of 2(R),3(E)-phytochromobilin derived from phycobiliproteins

• Published in: The Journal of biological chemistry Vol. 267; no. 21; pp. 14790 - 14798
• Main Authors: Cornejo, J. (Brown University, Providence, RI), Beale, S.I, Terry, M.J, Lagarias, J.C
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25-07-1992
• Subjects: Analytical, structural and metabolic biochemistry; AVENA SATIVA; Biliverdine - analogs & derivatives; Biliverdine - metabolism; Biological and medical sciences; Calothrix; Chromatography, High Pressure Liquid; Circular Dichroism; Cyanobacteria - metabolism; CYANOPHYTA; Electrophoresis, Polyacrylamide Gel; Fundamental and applied biological sciences. Psychology; Hydrolysis; Light-Harvesting Protein Complexes; LUMIERE; LUZ; Magnetic Resonance Spectroscopy; Methanol; Non metallic chromoproteins, photoproteins; Phytochrome - chemistry; Phytochrome - metabolism; PIGMENT; PIGMENTOS; Plant Proteins - metabolism; Porphyridium cruentum; Protein Conformation; PROTEINAS; PROTEINE; Proteins; Rhodophyta - metabolism; Spectrophotometry, Ultraviolet; Molecular structure; Calothrix; Circular dichroism spectrometry; Cyanobacteria; Phytochrome; Bacteria; Biological activity; Chromoprotein
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)42109-6

The unicellular rhodophyte, Porphyridium cruentum, and the filamentous cyanobacterium, Calothrix sp. PCC 7601, contain phycobiliproteins that have covalently bound phycobilin chromophores. Overnight incubation of solvent-extracted cells at 40 degrees C with methanol liberates free phycobilins that are derived from the protein-bound bilins by methanolytic cleavage of the thioether linkages between bilin and apoprotein. Two of the free bilins were identified as 3(E)-phycocyanobilin and 3(E)-phycoerythrobilin by comparative spectrophotometry and high pressure liquid chromatography. Methanolysis also yields a third bilin free acid whose absorption and 1H NMR spectra support the assignment of the 3(E)-phytochromobilin structure. This novel bilin is the major pigment isolated from cells that are pre-extracted with acetone-containing solvents. Since phytochrome- or phytochromobilin-containing proteins are not present in either organism, the 3(E)-phytochromobilin must arise by oxidation of phycobilin chromophores. This pigment is not obtained by similar treatment of a cyanobacterium and a rhodophyte that lack phycoerythrin. Therefore, 3(E)-phytochromobilin appears to be derived from phycoerythrobilin-containing proteins. Comparative CD spectroscopy of 3(E)-phytochromobilin and 3(E)-phycocyanobilin suggests that the two bilins share the R stereochemistry at the 2-position in the reduced pyrrole ring. Incubation of 2(R),3(E)-phytochromobilin with recombinant oat apophytochrome yields a covalent bilin adduct that is photoactive and spectrally indistinguishable from native oat phytochrome isolated from etiolated seedlings. These results establish that the phycobiliprotein-derived 2(R),3(E)-phytochromobilin is a biologically active phytochrome chromophore precursor