Modeling of variant copies of subunit D1 in the structure of photosystem II from Thermosynechococcus elongatus

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In the cyanobacterium Thermosynechococcus elongatus BP-1, living in hot springs, the light environment directly regulates expression of genes that encode key components of the photosynthetic multi-subunit protein-pigment complex photosystem II (PSII). Light is not only essential as an energy source to power photosynthesis, but leads to formation of aggressive radicals which induce severe damage of protein subunits and organic cofactors. Photosynthetic organisms develop several protection mechanisms against this photo-damage, such as the differential expression of genes coding for the reaction center subunit D1 in PSII. Testing the expression of the three different genes (psbAI, psbAII, psbAIII) coding for D1 in T. elongatus under culture conditions used for preparing the material used in crystallization of PSII showed that under these conditions only subunit PsbA1 is present. However, exposure to high-light intensity induced partial replacement of PsbA1 with PsbA3. Modeling of the variant amino acids of the three different D1 copies in the 3.0 Å resolution crystal structure of PSII revealed that most of them are in the direct vicinity to redox-active cofactors of the electron transfer chain. Possible structural and mechanistic consequences for electron transfer are discussed.DFG, SFB 498, Protein-Kofaktor-Wechselwirkungen in biologischen ProzessenEC/FP6/516510/EU/Linking molecular genetics and bio-mimetic chemistry - a multidisciplinary approach to achieve renewable hydrogen production/SOLAR-

Tocopherol cyclases : substrate specificity and phylogenetic relations

In the present studies, we focused on substrate specificity of tocopherol cyclase, the key enzyme in the biosynthesis of the tocopherols and plastochromanol-8, the main plant lipid antioxidants, with special emphasis on the preference for tocopherols and plastochromanol-8 precursors, taking advantage of the recombinant enzyme originating from Arabidopsis thaliana and isolated plastoglobules, thylakoids and various model systems like micelles and thylakoids. Plastoglobules and triacylglycerol micelles were the most efficient reaction environment for the cyclase. In various investigated systems, synthesis of γ-tocopherol proceeded considerably faster than that of plastochromanol-8, probably mainly due to different localization of the corresponding substrates in the analyzed lipid structures. Moreover, our study was complemented by bioinformatics analysis of the phylogenetic relations of the cyclases and sequence motifs, crucial for the enzyme activity, were proposed. The analysis revealed also a group of tocopherol cyclase-like proteins in a number of heterotrophic bacterial species, with a conserved region common with photosynthetic organisms, that might be engaged in the catalytic activity of both groups of organisms

Stern-Volmer plots of prenylquinols fluorescence quenching.

<p>The quenching was performed in egg yolk (EYL) or thylakoid lipid (TL) liposomes by trochloroacetic acid (TCA), trichlorobutyric acid (TCB), TCA ester of 8-hydroxyoctanoic acid (TC-C8) and TCA ester of 12-hydroxydodecanoid acid (TC-C12) sodium salts. Prenyllipid/membrane lipid molar proportion was 1/10.</p

Analysis of selected strains of cyanobacteria and <i>Phaeodactylum tricornutum</i> for the presence of α-Toc and PC-8.

<p>Analysis of selected strains of cyanobacteria and <i>Phaeodactylum tricornutum</i> for the presence of α-Toc and PC-8.</p

The content of tocopherol cyclase substrates in <i>vte1 Arabidopsis</i> mutant in leaves and chloroplast fractions used for the determination of tocopherol cyclase activity.

<p>The content of tocopherol cyclase substrates in <i>vte1 Arabidopsis</i> mutant in leaves and chloroplast fractions used for the determination of tocopherol cyclase activity.</p

Content of prenyllipids in selected green algae and maize leaves.

<p>Content of prenyllipids in selected green algae and maize leaves.</p

Fluorescence quantum yield (<i>ϕ</i>) of PQH₂-4 in solvents of different polarity.

<p>Fluorescence quantum yield (<i>ϕ</i>) of PQH₂-4 in solvents of different polarity.</p

The conserved aminoacid residues of tocopherol cyclases from the photosynthetic organisms shown in Fig 3, marked on the sequence of <i>A</i>. <i>thaliana</i>.

<p>In the analysis, bacterial sequences were excluded. An asterisk indicates fully conserved residue. A colon marks residues with strongly similar properties. A period indicates residues with weakly similar properties. The analysis was performed using Clustal Omega algorithm. Fully conserved aminoacids were highlighted in yellow or green (the most conserved region probably engaged in the catalytic reaction).</p

The unrooted phylogenetic tree of tocopherol cyclase sequences from different organisms.

<p>Bacterial proteins similar to tocopherol cyclase are included as an out-group. Blue- cyanobacteria, green—higher plants, yellow—green algae, red—red algae, pink—diatoms, gray—bacteria.</p

Relative fluorescence intensity of the prenylquinols in different lipid systems.

<p>Relative fluorescence intensity of the prenylquinols in different lipid systems.</p