Chlorophyll (Chl) a/b-binding proteins from Prochlorothrix hollandica known as Pcb antennae were studied by femtosecond transient absorption technique to identify energy transfer rates and pathways in Pcb and Pcb-PS I complexes. Carotenoids transfer energy to Chl with low efficiency of approximately 25% in Pcb complexes. Interestingly, analysis of transient absorption spectra identified a pathway from the hot S(1) state of zeaxanthin and/or beta-carotene as the major energy transfer channel between carotenoids and chlorophylls in Pcb whereas the S(2) state contributes only marginally to energy transfer. Due to energetic reasons, no energy transfer is possible via the relaxed S(1) state of carotenoids. The low overall energy transfer efficiency of carotenoids recognizes chlorophylls as the main light-harvesting pigments. Besides Chl a, presence of Chl b, which transfers energy to Chl a with nearly 100% efficiency, significantly broadens the spectral range accessible for light-harvesting and improves cross section of Pcb complexes. The major role of carotenoids in Pcb is photoprotection.
- MeSH
- chlorofyl a MeSH
- chlorofyl chemie MeSH
- fluorescenční spektrometrie MeSH
- fotosystém I (proteinový komplex) chemie metabolismus MeSH
- karotenoidy chemie MeSH
- přenos energie MeSH
- Prochlorothrix enzymologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl a MeSH
- chlorofyl MeSH
- chlorophyll b MeSH Prohlížeč
- fotosystém I (proteinový komplex) MeSH
- karotenoidy MeSH
The freshwater filamentous green oxyphotobacterium Prochlorothrix hollandica is an unusual oxygenic photoautotrophic cyanobacterium differing from most of the others by the presence of light-harvesting Pcb antenna binding both chlorophylls a and b and by the absence of phycobilins. The pigment-protein complexes of P. hollandica SAG 10.89 (CCAP 1490/1) were isolated from dodecylmaltoside solubilized thylakoid membranes on sucrose density gradient and characterized by biochemical, spectroscopic and immunoblotting methods. The Pcb antennae production is suppressed by high light conditions (>200 mumol photons m(-2) s(-1)) in P. hollandica. PcbC protein was found either in higher oligomeric states or coupled to PS I (forming antenna rings around PS I). PcbA and PcbB are most probably only very loosely bound to photosystems; we assume that these pigment-protein complexes function as low light-induced mobile antennae. Further, we have detected alpha-carotene in substantial quantities in P. hollandica thylakoid membranes, indicating the presence of chloroplast-like carotenoid synthetic pathway which is not present in common cyanobacteria.
- MeSH
- elektroforéza v polyakrylamidovém gelu MeSH
- fotosyntéza fyziologie MeSH
- fotosystém I (proteinový komplex) izolace a purifikace metabolismus MeSH
- fotosystém II (proteinový komplex) izolace a purifikace metabolismus MeSH
- gelová chromatografie MeSH
- imunoblotting MeSH
- Prochlorophytes metabolismus MeSH
- Prochlorothrix metabolismus MeSH
- světlo MeSH
- tylakoidy metabolismus ultrastruktura MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém I (proteinový komplex) MeSH
- fotosystém II (proteinový komplex) MeSH
Prochlorothrix hollandica is one of the three known species of an unusual clade of cyanobacteria (formerly called "prochlorophytes") that contain chlorophyll a and b molecules bound to intrinsic light-harvesting antenna proteins. Here, we report the structural characterization of supramolecular complex consisting of Photosystem I (PSI) associated with the chlorophyll a/b-binding Pcb proteins. Electron microscopy and single particle image analysis of negatively stained preparations revealed that the Pcb-PSI supercomplex consists of a central trimeric PSI surrounded by a ring of 18 Pcb subunits. We conclude that the formation of the Pcb ring around trimeric PSI represents a mechanism for increasing the light-harvesting efficiency in chlorophyll b-containing cyanobacteria.
- MeSH
- centrifugace - gradient hustoty MeSH
- elektronová mikroskopie MeSH
- fotosystém I (proteinový komplex) ultrastruktura MeSH
- kvarterní struktura proteinů MeSH
- Prochlorothrix ultrastruktura MeSH
- světlosběrné proteinové komplexy chemie ultrastruktura MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém I (proteinový komplex) MeSH
- světlosběrné proteinové komplexy MeSH
