Carotenoids, versatile components of oxygenic photosynthesis

Abstract

Carotenoids (CARs) are a group of pigments that perform several important physiological functions in all kingdoms of living organisms. CARs serve as protective agents, which are essential structural components of photosynthetic complexes and membranes, and they play an important role in the light harvesting mechanism of photosynthesizing plants and cyanobacteria. The protection against reactive oxygen species, realized by quenching of singlet oxygen and the excited states of photosensitizing molecules, as well as by the scavenging of free radicals, is one of the main biological functions of CARs. X-ray crystallographic localization of CARs revealed that they are present at functionally and structurally important sites of both the PSI and PSII reaction centers. Characterization of a CAR-less cyanobacterial mutant revealed that while the absence of CARs prevents the formation of PSII complexes, it does not abolish the assembly and function of PSI. CAR molecules assist in the formation of protein subunits of the photosynthetic complexes by gluing together their protein components. In addition to their aforementioned indispensable functions, CARs have a substantial role in the formation and maintenance of proper cellular architecture, and potentially also in the protection of the translational machinery under stress conditions.

Keywords: (E)-1-hydroxy-2-methyl-2-butenyl diphosphate; 1-deoxy-d-xylulose 5-phosphate; 1-deoxy-d-xylulose 5-phosphate reducto-isomerase; 1-deoxy-d-xylulose 5-phosphate synthase; 15-cis-ζ-carotene isomerase; 2-C-methyl-d-erythritol 2,4-cyclodiphosphate; 2-C-methyl-d-erythritol 4-phosphate; 2′-O-glycosyltransferase; 4-(citidine 5′-diphospho)-2-C-methyl-d-erythritol; AACT; ADP; APC; ATP; BChl; C-18 hydroxylase; CAR; CDP-ME2P; CHYβ; CHYε; CMP; CP43; CP43-less CP47-containing reaction center of PSII; CP47; CTP; Carotenoid synthesis; Carotenoid–lipid interaction; Chl; CrtB; CrtH; CrtI; CrtISO; CrtL; CrtO; CrtP; CrtQ; CrtR; CrtW; CruA; CruE; CruF; CruG; CruH; CruP; DDE; DEP; DMAPP; DXP; DXR; DXS; Ddx; Dtx; EF-G; GAP; GGPP; HMBDP; HMG-CoA; HMG-CoA reductase; HMGR; IPP; LCYβ; LCYε; LHC; LHCI; LHCII; LHCSR; MECDP; MEP; MVA; Membrane structure; NADP(+); NADPH; NPQ; NSY; OCP; PCP; PDS; PSI; PSII; PSY; Photosynthesis; RC47; ROS; VDE; Z-ISO; ZDS; ZEP; acetoacetyl-CoA thiolase; adenosine diphosphate; adenosine triphosphate; allophycocyanin; bacterial type carotene isomerase; bacteriochlorophyll; carotene β-hydroxylase; carotene β-ketolase; carotenoid; chlorophyll; chlorophyll–protein complex 43; chlorophyll–protein complex 47; cis-to-trans carotenoid isomerase; cytidine monophosphate; cytidine triphosphate; d-glyceraldehyde 3-phosphate; diadinoxanthin; diadinoxanthin de-epoxidase; diatoxanthin epoxidase; diatoxathin; dimethylallyl diphosphate; elongation factor G; geranylgeranyl diphosphate; isopentenyl diphosphate; light harvesting complex; light harvesting complex of PSI; light harvesting complex of PSII; light harvesting stress response protein; lycopene cyclase; lycopene β-cyclase; lycopene ε-cyclase; methylerythritol phosphate; mevalonic acid; neoxanthin synthase; nicotinamide adenine dinucleotide phosphate; non-photochemical quenching; orange carotenoid protein; peridinin–Chl a protein; photosystem I; photosystem II; phytoene desaturase; phytoene synthase; reactive oxygen species; reduced nicotinamide adenine dinucleotide phosphate; violaxanthin de-epoxidase; zeaxanthin epoxidase; β-carotene desaturase/methyltransferase; β-hydroxy-β-methylglutaryl-CoA; β-hydroxylase; γ-carotene 1′-hydroxylase; ε-hydroxylase; ζ-carotene desaturase.