title: Effects of ultraviolet-B radiation on phycobilisomes of Synechococcus PCC 7942: alterations in conformation and energy transfer characteristics.
abstract: Phycobilisomes (PBS), the major light harvesting antenna of the cyanobacterium Synechococcus contain phycocyanin (PC) and allophycocyanin (APC) as major pigment-protein complexes. PBS also absorb ultraviolet-B (280-320 nm) radiation. Exposure of Synechococcus PBS to low dose of UV-B (approximately 0.28 mw.cm-2) for 90 min induced change in absorption, emission and excitation characteristics of PBS and these changes got enhanced after 3 h of exposure. Room temperature excitation and emission spectra clearly indicated uncoupling of energy transfer from PC to APC on exposure to UV-B. Also, the 77K emission spectra suggested that F682 emission originating from APC decreased by 42% after 3 h of exposure. Circular dichroism (CD) spectra of UV-B exposed PBS indicated changes (14% decrease) in the alpha-helical content after 90 min treatment. SDS-PAGE analysis indicated degradation of a 75 kDa polypeptide (which appear to be a linker polypeptide) on UV-B treatment. The degradation of this polypeptide seems to induce changes in pigment-protein interaction and decoupling of energy transfer within the PBS. Our results for the first time clearly indicate that the PBS of Synechococcus are targets for UV-B damage.
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
authors.forename: J F
authors.initials: JF
authors.lastname: Sah
authors.forename: K B
authors.initials: KB
authors.lastname: Krishna
authors.forename: M
authors.initials: M
authors.lastname: Srivastava
authors.forename: P
authors.initials: P
authors.lastname: Mohanty
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000528:radiation effects*; D000458:Cyanobacteria / Q000528:radiation effects*; D004735:Energy Transfer / Q000528:radiation effects*; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D010798:Phycocyanin / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry / Q000528:radiation effects*; D017433:Protein Structure, Secondary / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D014466:Ultraviolet Rays
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D010940:Plant Proteins; C002497:allophycocyanin; D010798:Phycocyanin