Photosystem II (PSII) is a multisubunit protein complex in cyanobacteria, algae and plants that use light energy for oxidation of water and reduction of plastoquinone. The conversion of excitation energy absorbed by chlorophylls into the energy of separated charges and subsequent water-plastoquinone oxidoreductase activity are inadvertently coupled with the formation of reactive oxygen species (ROS). Singlet oxygen is generated by the excitation energy transfer from triplet chlorophyll formed by the intersystem crossing from singlet chlorophyll and the charge recombination of separated charges in the PSII antenna complex and reaction center of PSII, respectively. Apart to the energy transfer, the electron transport associated with the reduction of plastoquinone and the oxidation of water is linked to the formation of superoxide anion radical, hydrogen peroxide and hydroxyl radical. To protect PSII pigments, proteins and lipids against the oxidative damage, PSII evolved a highly efficient antioxidant defense system comprising either a non-enzymatic (prenyllipids such as carotenoids and prenylquinols) or an enzymatic (superoxide dismutase and catalase) scavengers. It is pointed out here that both the formation and the scavenging of ROS are controlled by the energy level and the redox potential of the excitation energy transfer and the electron transport carries, respectively. The review is focused on the mechanistic aspects of ROS production and scavenging by PSII. This article is part of a Special Issue entitled: Photosystem II.

• MeSH
• fotosystém II - proteinový komplex chemie   metabolismus   MeSH
• molekulární modely MeSH
• oxidace-redukce MeSH
• přenos energie MeSH
• reaktivní formy kyslíku metabolismus   MeSH
• scavengery volných radikálů metabolismus   MeSH
• transport elektronů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

The selective replacement of photodamaged D1 protein within the multisubunit photosystem II (PSII) complex is an important photoprotective mechanism in chloroplasts and cyanobacteria. FtsH proteases are involved at an early stage of D1 degradation, but it remains unclear how the damaged D1 subunit is recognized, degraded, and replaced. To test the role of the N-terminal region of D1 in PSII biogenesis and repair, we have constructed mutants of the cyanobacterium Synechocystis sp PCC 6803 that are truncated at the exposed N terminus. Removal of 5 or 10 residues blocked D1 synthesis, as assessed in radiolabeling experiments, whereas removal of 20 residues restored the ability to assemble oxygen-evolving dimeric PSII complexes but inhibited PSII repair at the level of D1 degradation. Overall, our results identify an important physiological role for the exposed N-terminal tail of D1 at an early step in selective D1 degradation. This finding has important implications for the recognition of damaged D1 and its synchronized replacement by a newly synthesized subunit.

• MeSH
• autotrofní procesy účinky léků   účinky záření   MeSH
• biologické modely MeSH
• dimerizace MeSH
• financování organizované MeSH
• fluorescenční spektrometrie MeSH
• fotosystém II - proteinový komplex genetika   chemie   MeSH
• linkomycin farmakologie   MeSH
• molekulární sekvence - údaje MeSH
• mutace genetika   MeSH
• mutantní proteiny metabolismus   MeSH
• podjednotky proteinů chemie   metabolismus   MeSH
• posttranslační úpravy proteinů účinky léků   účinky záření   MeSH
• sekundární struktura proteinů MeSH
• sekvence aminokyselin MeSH
• světlo MeSH
• Synechocystis MeSH
• tylakoidy metabolismus   účinky léků   účinky záření   MeSH
• vztahy mezi strukturou a aktivitou MeSH