Near-atomic cryo-EM structure of the light-harvesting complex LH2 from the sulfur purple bacterium Ectothiorhodospira haloalkaliphila.

Bacteria with the simplest system for solar energy absorption and conversion use various types of light-harvesting complexes for these purposes. Light-harvesting complex 2 (LH2), an important component of the bacterial photosynthetic apparatus, has been structurally well characterized among purple non-sulfur bacteria. In contrast, so far only one high-resolution LH2 structure from sulfur bacteria is known.

LH2 Complex from Sulfur Bacteria Allochromatium vinosum - Natural Singlet Oxygen Sensor.

It was established that in a heterogeneous model system, which consisted of two types of complexes: reaction center or core complex of photosystem 2 of higher plants and LH2 complex of the sulfur bacterium Alc. vinosum, BChl850 oxidation of the LH2 complex could be observed under illumination by the light at a wavelength of 662 nm, which is the red absorption band of Chl. It has been shown that this process induces release of singlet oxygen, which is generated in photosystem II complexes and then partially diffuses into LH2 complex, where it oxidizes BChl850.

Selective Excitation of Carotenoids of the Allochromatium vinosum Light-Harvesting LH2 Complexes Leads to Oxidation of Bacteriochlorophyll.

The mechanism of bacteriochlorophyll photooxidation in light-harvesting complexes of a number of purple photosynthetic bacteria when the complexes are excited into the carotenoid absorption bands remains unclear for many years. Here, using narrow-band laser illumination we measured action spectrum of this process for the spectral ranges of carotenoid and bacteriochlorophyll. It is shown that bacteriochlorophyll excitation results in almost no photooxidation of these molecules, while carotenoid excitation leads to oxidation with quantum yield of about 0,0003.

Disproportionate effect of cationic antiseptics on the quantum yield and fluorescence lifetime of bacteriochlorophyll molecules in the LH1-RC complex of R. rubrum chromatophores.

Photosynthetic membrane complexes of purple bacteria are convenient and informative macromolecular systems for studying the mechanisms of action of various physicochemical factors on the functioning of catalytic proteins both in an isolated state and as part of functional membranes. In this work, we studied the effect of cationic antiseptics (chlorhexidine, picloxydine, miramistin, and octenidine) on the fluorescence intensity and the efficiency of energy transfer from the light-harvesting LH1 complex to the reaction center (RC) of Rhodospirillum rubrum chromatophores. The effect of antiseptics on the fluorescence intensity and the energy transfer increased in the following order: chlorhexidine, picloxydine, miramistin, octenidine.