- Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants’ survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state.
- Phytol is the isoprenoid alcohol bound in ester linkage to chlorophyll, the most abundant photosynthetic pigment in plants. During leaf senescence, large amounts of phytol are released by chlorophyll degradation. However, the pathway of phytol catabolism in plants is unknown. We hypothesized that phytol degradation in plants might involve its oxidation into the long-chain aldehyde phytenal. Using GC-MS for aldehyde quantification after derivatization with methylhydroxylamine, phytenal was identified in leaves, whereas other long-chain aldehydes (phytanal and pristanal) were barely detectable.
- Ferrochelatase (FeCh) is an essential enzyme catalyzing the synthesis of heme. Interestingly, in cyanobacteria, algae, and plants, FeCh possesses a conserved transmembrane chlorophyll a/b binding (CAB) domain that resembles the first and the third helix of light-harvesting complexes, including a chlorophyll-binding motif. Whether the FeCh CAB domain also binds chlorophyll is unknown. Here, using biochemical and radiolabeled precursor experiments, we found that partially inhibited activity of FeCh in the cyanobacterium Synechocystis PCC 6803 leads to overproduction of chlorophyll molecules that accumulate in the thylakoid membrane and, together with carotenoids, bind to FeCh.
- Chlorophylls (Chls) are the most important cofactors for capturing solar energy to drive photosynthetic reactions. Five spectral types of Chls have been identified to date, with Chl f having the most red-shifted absorption maximum because of a C21-formyl group substitution of Chl f. However, the biochemical provenance of this formyl group is unknown. Here, we used a stable isotope labeling technique (18O and 2H) to determine the origin of the C21-formyl group of Chl f and to verify whether Chl f is synthesized from Chl a in the cyanobacterial species Halomicronema hongdechloris.
- Genetic and genomic studies indicate that copper deficiency triggers changes in the expression of genes encoding key enzymes in various chloroplast-localized lipid/pigment biosynthetic pathways. Among these are CGL78 involved in chlorophyll biosynthesis and HPPD1, encoding 4-hydroxyphenylpyruvate dioxygenase catalyzing the committed step of plastoquinone and tocopherol biosyntheses. Copper deficiency in wild-type cells does not change the chlorophyll content, but a survey of chlorophyll protein accumulation in this situation revealed increased accumulation of LHCSR3, which is blocked at the level of mRNA accumulation when either CGL78 expression is reduced or in the crd1 mutant, which has a copper-nutrition conditional defect at the same step in chlorophyll biosynthesis.
- The genomes uncoupled 4 (GUN4) protein is a nuclear-encoded, chloroplast-localized, porphyrin-binding protein implicated in retrograde signaling between the chloroplast and nucleus, although its exact role in this process is still unclear. Functionally, it enhances Mg-chelatase activity in the chlorophyll biosynthesis pathway. Because GUN4 is present only in organisms that carry out oxygenic photosynthesis and because it binds protoporphyrin IX (PPIX) and Mg-PPIX, it has been suggested that it prevents production of light- and PPIX- or Mg-PPIX-dependent reactive oxygen species.
- Background: In plants, a key regulatory step in chlorophyll biosynthesis is catalyzed by two light-dependent isozymes.Results: The two isozymes operate via the same reaction mechanism but differ in their catalytic efficiencies.Conclusion: Different substrate affinities and conformational flexibilities modulate the catalytic reaction.Significance: Detailed understanding of light-driven reactions in nature has a big impact on the development of artificial energy conversion systems.
- Background: The Gun4 protein stimulates activity of magnesium chelatase, and it is important for chlorophyll biosynthesis.Results: Mechanism of porphyrin binding by Gun4 was proposed, and a Gun4 mutant was characterized in detail.Conclusion: Gun4 controls substrate channeling into chlorophyll biosynthesis.Significance: In silico, in vitro, and in vivo data were integrated to explain the function of Gun4 protein.
- The tetratricopeptide repeat (TPR)-containing protein FLU is a negative regulator of chlorophyll biosynthesis in plants. It directly interacts through its TPR domain with glutamyl-tRNA reductase (GluTR), the rate-limiting enzyme in the formation of δ-aminolevulinic acid (ALA). Delineation of how FLU binds to GluTR is important for understanding the molecular basis for FLU-mediated repression of synthesis of ALA, the universal tetrapyrrole precursor. Here, we characterize the FLU-GluTR interaction by solving the crystal structures of the uncomplexed TPR domain of FLU (FLUTPR) at 1.45-Å resolution and the complex of the dimeric domain of GluTR bound to FLUTPR at 2.4-Å resolution.