Assembly Of Pigment-protein Complexes Research Articles

Carotenogenesis in cyanobacteria: CruA/CruP-type and CrtL-type lycopene cyclases.

Cyanobacteria are oxygenic photoautotrophic prokaryotes containing chlorophylls and carotenoids, and the latter play important roles in light-harvesting, protection of excess light, assembly of pigment-protein complexes, and stabilization of lipid membranes. Cyanobacteria produce many kinds of carotenoids, such as β-carotene, zeaxanthin, echinenone, and myxol glycosides, which have a cyclic structure at one or both end(s). Cyclization of lycopene is a branch point in carotenoid biosynthesis to β-carotene and γ-carotene. Two types of lycopene cyclases, CruA/CruP-type and CrtL-type, are functionally confirmed in only five species, while homologous genes are found in the genomes of most cyanobacteria. This review summarizes the carotenogenesis pathways and the functional enzymes along with genes, focusing particularly on the cyclization of lycopene by distinct types of lycopene cyclases in cyanobacteria.

Interdependence of carotenoid biosynthesis and assembly of pigment-protein complexes in Ectothiorhodospira haloalkaliphila cells

In the majority of species of photosynthetic bacteria, the lightharvesting antenna consists of two typesof pigment–protein complexes—peripheral LH2 andnearcentral LH1—which are located in the innercytoplasmic membrane [1]. The LH1 complex surrounds the reaction center (RC), forming a “core”complex with it (or the LH1–RC complex). Bothlightharvesting complexes were obtained in the pureform and are well studied [2–6]. Depending on thespecies of bacteria, the LH1 complex has the majorabsorption maximum at ~865–890 nm in the nearinfrared region of the spectrum, whereas the LH2 complex has two maxima (at ~800 and ~850 nm) [2, 3]. Inthe purple bacteria, these complexes are constructedaccording to a similar modular principle and consist oftwo types of polypeptides (α and β), bacteriochlorophyll (BChl), and carotenoids [4–6]. Carotenoids areadditional pigments. They perform several importantfunctions in vivo (lightharvesting, protecting, andstructural functions) [7, 8]. It was stated that the LH2complexes are not assembled in the cells of carotenoidless mutants of purple nonsulfur bacteria [9].There is another approach to obtaining carotenoidless LH2 complexes—the use of an inhibitor ofcarotenogenesis during cell culturing. Using theinhibitor diphenylamine (DPA), we obtained carotenoidless cells (DPA cells) of the purple sulfur bacterium

Chlorophyll biosynthesis and chloroplast development in etiolated seedlings of Ginkgo biloba L.

Ginkgo biloba L. is a large tree native in China with evolutionary affinities to the conifers and cycads. However unlike conifers, the gymnosperm G. biloba is not able to synthesize chlorophyll (Chl) in the dark, in spite of the presence of genes encoding subunits of light-independent protochlorophyllide oxidoreductase (DPOR) in the plastid genome. The principal aims of the present study were to investigate the presence of DPOR protein subunits (ChlL, ChlN, ChlB) as well as the key regulatory step in Chl formation: aminolevulinic acid (ALA) synthesis and abundance of the key regulatory enzyme in its synthesis: glutamyl-tRNA reductase (GluTR). In addition, functional stage of photosynthetic apparatus and assembly of pigment-protein complexes were investigated. Dark-grown, illuminated and circadian-grown G. biloba seedlings were used in our experiments. Our results clearly showed that no protein subunits of DPOR were detected irrespective of light conditions, what is consistent with the absence of Chl and Chl-binding proteins (D1, LHCI, LHCIIb) in the dark. This correlates with low ALA-synthesizing capacity and low amount of GluTR. The concentration of protochlorophyllide (Pchlide) in the dark is low and non-photoactive form (Pchlide633) was predominant. Plastids were developed as typical etioplasts with prollamelar body and few prothylakoid membranes. Continual illumination (24 h) only slightly stimulated ALA and Chl synthesis, although Pchlide content was reduced. Prollamelar bodies disappeared, but no grana were formed, what was consistent with the absence of D1, LHCI, LHCIIb proteins. Lightinduced development of photosynthetic apparatus is extremely slow, as indicated by Chl fluorescence and gas exchange measurements. Even after 72 h of continuous illumination, the values of maximum (Fv/Fm) and effective quantum yield (ΦPSII) and rate of net photosynthesis (PN) did not reach the values comparable with circadian-grown plants.

Assembly of pigment-protein complexes in carotenoid-deficient membranes of plastids from wheat seedlings treated with norflurazon.

The pyridazinone-type herbicide norflurazon SAN 9789 inhibiting the biosynthesis of long-chain carotenoids results in significant decrease in PS II core complexes and content of light-harvesting complex (LHC) polypeptides. At the same time, early light-induced proteins (ELIP) with molecular masses of 20.5-16.5 and 13.5 kD disappear in norflurazon-treated seedlings grown under intermittent (pulsed) light, confirming the hypothesis that they are carotenoid-binding proteins. Full disappearance of Chl a forms at 668, 676, and 690 nm and a sharp decrease in Chl b form at 648 nm in treated seedlings grown under 30 or 100 lx light intensity shows close contact of these forms with carotenoids in the thylakoid membrane. The band shift from 740 to 720 nm in the low-temperature fluorescence spectrum (77 K) suggests a disturbance of energy transfer from LHC to the Chl a form at 710-712 nm.

Effect of oxygen on translation and posttranslational steps in expression of photosynthesis genes in Rhodobacter capsulatus.

The formation of the photosynthetic apparatus in Rhodobacter capsulatus is regulated by oxygen tension. Previous studies have shown a regulatory effect of oxygen on the transcription of photosynthesis genes and on the stability of certain mRNA segments. Here we show that oxygen affects puf and puc gene expression posttranslationally and that this regulation depends on the presence of bacteriochlorophyll. Our data suggest that this posttranslational effect of oxygen on puf and puc expression is due to the primary effect of oxygen on bacteriochlorophyll synthesis or assembly of pigment protein complexes. Oxygen does not affect the rates of translation of puf-encoded proteins.

The influence of bacteriochlorophyll biosynthesis on formation of pigment-binding proteins and assembly of pigment protein complexes in Rhodopseudomonas capsulata

The synthesis of bacteriochlorophyll (Bchl) was inhibited in wild type strain of Rhodopseudomonas capsulata by levulinic acid (LA), δ-aminolevulinic acid of α,α′-dipyridyl. The transcription of genes for pigment-binding proteins, the synthesis and incorporation of these proteins into the membrane and the assembly of photosynthetic complexes were studied. Inhibition of Bchl synthesis did not impair formation of mRNA for pigment-binding polypeptides, but inhibited the synthesis of these proteins as well as stable incorporation into the membrane. The results let suggest, that Bchl is necessary for the stabilization of pigment-binding proteins in the membrane, and that intermediates of Bchl-synthesis affect the synthesis of these proteins. The same experiments were carried out with mutant strains blocked in Bchl synthesis. All Bchl-less mutant strains investigated here, showed transcription of photosynthetic genes at a rate which was independent of oxygen tension. The synthesis of polypeptides of reaction center, B870 and B800-850 complexes were differently affected by blocks in Bchl-synthesis. LA inhibited the synthesis of pigment-binding proteins in mutant strains similarly as in wild-type strain.