Photosynthetic organisms have developed multiple protective mechanisms to survive under high-light conditions. In plants, one of these is the thermal dissipation excitation energy in membrane-bound chlorophyll antenna photosystem II. The question whether or not cyanobacteria, progenitor chloroplast, an equivalent photoprotective mechanism has long been unanswered. Recently, however, evidence was presented for possible existence a dissipating excess absorbed phycobilisome, extramembrane...

Intense sunlight is dangerous for photosynthetic organisms. Cyanobacteria, like plants, protect themselves from light-induced stress by dissipating excess absorbed energy as heat. Recently, it was discovered that a soluble orange carotenoid protein, the OCP, essential this photoprotective mechanism. Here we show OCP also member of family photoactive proteins; unique example protein containing photoresponsive chromophore. Upon illumination with blue-green light, undergoes reversible...

Protection from too much light Photosynthetic organisms protect themselves using pigment photoswitches that absorb excess energy. Leverenz et al. analyzed the structure of an active, energy-dissipating form orange carotenoid protein (OCP) a cyanobacterium. When activated by light, OCP moves its hydrophobic 12 Å within to accommodate nonphotochemical quenching broader photosynthetic antenna complex. Science , this issue p. 1463

We studied the effect of UV-B radiation (280−320 nm) on donor- and acceptor-side components photosystem II in cyanobacterium Synechocystis sp. PCC 6803 by measuring relaxation flash-induced variable chlorophyll fluorescence. irradiation increases t1/2 decay assigned to reoxidation QA- QB from 220 330 μs centers which have site occupied, 3 6 ms with empty. In contrast, slow component arising recombination QAQB- state S2 water-oxidizing complex decreases 13 1−2 s. presence DCMU, fluorescence...

In conditions of fluctuating light, cyanobacteria thermally dissipate excess absorbed energy at the level phycobilisome, light-collecting antenna. The photoactive Orange Carotenoid Protein (OCP) and Fluorescence Recovery (FRP) have essential roles in this mechanism. Absorption blue-green light converts stable orange (inactive) OCP form found darkness into a metastable red (active) form. Using an vitro reconstituted system, we studied interactions between OCP, FRP, phycobilisomes demonstrated...

The photoprotective processes of photosynthetic organisms involve the dissipation excess absorbed light energy as heat. Photoprotection in cyanobacteria is mechanistically distinct from that plants; it involves orange carotenoid protein (OCP), a water-soluble containing single carotenoid. OCP new member family blue light-photoactive proteins; blue-green triggers OCP-mediated response. Here we report structural and functional characterization wild type two mutant forms OCP, model organism...

In cyanobacteria, activation of the Orange Carotenoid Protein (OCP) by intense blue-green light triggers photoprotective thermal dissipation excess absorbed energy leading to a decrease (quenching) fluorescence harvesting phycobilisomes and, concomitantly, arriving reaction centers. Using spectrally resolved picosecond fluorescence, we have studied cells wild-type Synechocystis sp. PCC 6803 and mutants without with extra OCP (ΔOCP OverOCP) both in unquenched quenched state. With use target...

High light can be lethal for photosynthetic organisms. Similar to plants, most cyanobacteria protect themselves from high irradiance by increasing thermal dissipation of excess absorbed energy. The photoactive soluble orange carotenoid protein (OCP) is essential the triggering this photoprotective mechanism. Light induces structural changes in and protein, leading formation a red active form. Through targeted gene interruption we have now identified that mediates recovery full antenna...

Abstract The orange carotenoid protein (OCP) serves as a sensor of light intensity and an effector phycobilisome (PB)–associated photoprotection in cyanobacteria. Structurally, the OCP is composed two distinct domains spanned by single chromophore. Functionally, response to high light, converts from dark-stable form, OCPO, active red OCPR. C-terminal domain has been implicated dynamic plays role switching off OCP's photoprotective through its interaction with fluorescence recovery protein....

Cyanobacteria have developed a photoprotective mechanism that decreases the energy arriving at photosynthetic reaction centers under high-light conditions. The photoactive orange carotenoid protein (OCP) is essential in this as light sensor and quencher. When OCP photoactivated by strong blue-green light, it able to dissipate excess heat interacting with phycobilisomes. As consequence, charge separation recombination leading formation of singlet oxygen diminishes. Here, we demonstrate has...

The orange carotenoid protein (OCP) is a two-domain photoactive that noncovalently binds an echinenone (ECN) and mediates photoprotection in cyanobacteria. In the dark, OCP assumes orange, inactive state known as OCPO; blue light illumination results red active state, OCPR. OCPR characterized by large-scale structural changes involve dissociation separation of C-terminal N-terminal domains accompanied translocation into domain. mechanistic dynamic-structural relations between photon...

Significance Protection from overexcitation is one of the most important requirements all photosynthetic organisms. Here we present a model based on coupled cross-linking/mass spectrometry and site-directed mutagenesis means by which orange carotenoid protein (OCP) binds to phycobilisome (PBS) antenna complex avoid photodamage. The shows that must actively burrow into complex, separating PBS rings in process. This penetration explains for first time, our knowledge, how OCP could approach...

Orange carotenoid protein (OCP) is a photoactive that mediates photoprotection in cyanobacteria. OCP binds different ketocarotenoid chromophores such as echinenone (ECN), 3′- hydroxyechinenone (hECN), and canthaxanthin (CAN). In the dark, an inactive orange form known OCPO; upon illumination, red active state formed, referred to OCPR, can interact with phycobilisome. Large gaps still exist mechanistic understanding of events between photon absorption formation OCPR state. Recent studies...

The thermophilic cyanobacterium, Thermosynechococcus elongatus, has been grown in the presence of Sr2+ instead Ca2+ with aim biosynthetically replacing oxygen-evolving enzyme Sr2+. Not only were cells able to grow normally Sr2+, they actively accumulated ion levels higher than those normal cultures. A protocol was developed purify a fully active Sr2+-containing photosystem II (PSII). modified contained polypeptide profile and 1 strontium/4 manganese, indicating that contains calcium/4...

Abstract In response to iron deficiency, cyanobacteria synthesize the stress–induced chlorophyll binding protein IsiA. This protects cyanobacterial cells against stress. It has been proposed that protective role of IsiA is related a blue light–induced nonphotochemical fluorescence quenching (NPQ) mechanism. iron-replete cell cultures, strong light known induce mechanism dissipates excess absorbed energy in phycobilisome, extramembranal antenna cyanobacteria. this photoprotective mechanism,...

In high light conditions, cyanobacteria dissipate excess absorbed energy as heat in the light-harvesting phycobilisomes (PBs) to protect photosynthetic system against photodamage. This process requires binding of red active form Orange Carotenoid Protein (OCPr), which can effectively quench excited state one allophycocyanin bilins. Recently, an vitro reconstitution was developed using isolated OCP and PBs from Synechocystis PCC 6803. Here we have used spectrally resolved picosecond...