Carotenoids in photosynthesis. I: Location in photosynthetic membranes and light-harvesting function

Trimeric forms of the photosystem I reaction center complex pre-exist in the membranes of the cyanobacterium Spirulina platensis.

Until now, the functional and structural characterization of monomeric photosystem 1 (PS1) complexes from Thermosynechococcus elongatus has been hampered by the lack of a fully intact PS1 preparation; for this reason, the three-dimensional crystal structure at 2.5 A resolution was determined with the trimeric PS1 complex [Jordan, P., et al. (2001) Nature 411 (6840), 909-917]. Here we show the possibility of isolating from this cyanobacterium the intact monomeric PS1 complex which preserves all subunits and the photochemical activity of the isolated trimeric complex. Moreover, the equilibrium between these complexes in the thylakoid membrane can be shifted by a high-salt treatment in favor of monomeric PS1 which can be quantitatively extracted below the phase transition temperature. Both monomers and trimers exhibit identical posttranslational modifications of their subunits and the same reaction centers but differ in the long-wavelength antenna chlorophylls. Their chlorophyll/P700 ratio (108 for the monomer and 112 for the trimer) is slightly higher than in the crystal structure, confirming mild preparation conditions. Interaction of antenna chlorophylls of the monomers within the trimer leads to a larger amount of long-wavelength chlorophylls, resulting in a higher photochemical activity of the trimers under red or far-red illumination. The dynamic equilibrium between monomers and trimers in the thylakoid membrane may indicate a transient monomer population in the course of biogenesis and could also be the basis for short-term adaptation of the cell to changing environmental conditions.

Structure and function of intact photosystem 1 monomers from the cyanobacterium Thermosynechococcus elongatus.

When isolating Photosystem 1 from the thylakoid membranes of cyanobacteria, a multiplicity of photosystem complexes can be encountered, which has not yet been observed in any other phototrophic organisms: After solubilisation of thylakoid membranes with detergents, trimeric, dimeric and monomeric forms of Photosystem 1 can be separated. The question must now be answered, which of the stable Photosystem 1 forms is the functional form in vivo-monomeric or trimeric? The two possibilities are discussed, though we mainly present arguments for the existence of the trimeric form of Photosystem 1 in cyanobacterial thylakoid membranes.

Does the trimeric form of the Photosystem 1 reaction center of cyanobacteria in vivo exist

Interactions between cholorophyllase, chlorophyll a, plant lipids and Mg2+

The influence of carotenoids on the conformation of chlorophyll-protein complexes isolated from the cyanobacterium Plectonema boryanum. Absorption and circular dichroism study

Degradation by means of enzymes can provide valuable information on the structure and spatial arrangement of pigment-protein complexes (Schmidt 1983, Suss et al. 1976, Jennings et al. 1979). A number of studies has been devoted to the influence of enzymes on thylakoid membranes or changes in polypeptide composition of the membranes. The results have shown that a number of peripheral proteins is digested virtually without residue, while proteins or pigment-protein complexes immersed into the matrix are degraded little or not at all. The main reason is probably inaccessibility of integral proteins to hydrophilic enzymes, which are incapable of penetrating the lipid bilayer. Our study was aimed at investigating the effect of hydrolytic enzymes on isolated pigment-protein complexes of photosystem 1 of cyanobacteria with the purpose of obtaining more information on the molecular organisation of this complex.

Effect of Hydrolytic Enzymes on Cyanobacterial Pigment-Protein Complexes of Photosystem 1

The influence of sodium-dodecylsulfate on the stability of cyanobacterial photosystem-1 pigment-protein complexes

The blue-green algaPlectonema boryanum was chosen for a study of the properties of rRNA of procaryotic organisms. The process of rRNA species maturation was studied by labelling RNA with the isotope 32P.23 S and 16 S rRNA molecules each have their own precursors. Molecules with molecular weights of 1.65 X 106 and 1.24xlO6 were identified as precursors of23 S rRNA, while the molecules 0.87 X 106; 0.78 X 106 and 0.68 X 106 were found to be precursors of the 16 S rRNA. No common polycistronic precursor could be found.

https://link.springer.com/content/pdf/10.1007%2FBF02922928.pdf

Maturation of ribosomal RNA in blue-green algae in light and darkness

We have recently isolated and characterised the PS 1 pigment-protein complexes (PPCs) from the cyanobacterium Plectonema boryanum (Hladik and Sofrova (1981)). Isolation procedure — extraction of thylakoid membranes by Triton X-100, followed by the chromatography on DEAE cellulose column — yields two fractions; first containing complex of Mr 260 000 (denoted as PPC III), the second containing complex of Mr 118 000 (denoted as PPC II). It was shown (Hladik et al. (1982)) that the quarternary structure of the PPC III protein is — at least partly — conserved : this complex was found to be the oligomer of PPC II. We have proved that specificaly oriented carotenoids (characterised by strong positive circular dichroism bands at 480 and 505 nm) mediate the substantial part of the interactions between the pigment-protein subunits. The presence of protein-fixed, chiraly arranged carotenoids in PPCs seems to be a more general property of these systems: they were found in bacteria (Cogdell et al. (1976)) and also in PPCs from higher plants (Schubin et al. (1981)). The aim of our work was to study the functional consequences of this structural feature of PS 1 complex.

Jiří Hladík

Papers

The influence of carotenoids on the conformation of chlorophyll-protein complexes isolated from the cyanobacterium Plectonema boryanum. Absorption and circular dichroism study

Effect of Hydrolytic Enzymes on Cyanobacterial Pigment-Protein Complexes of Photosystem 1

The influence of sodium-dodecylsulfate on the stability of cyanobacterial photosystem-1 pigment-protein complexes

Maturation of ribosomal RNA in blue-green algae in light and darkness

Luminescence Study of PS 1 Pigment-Protein Complexes Isolated from the Cyanobacterium Plectonema Boryanum