Certain cyanobacteria synthesize chlorophyll (Chl) molecules (Chl d and Chl f) that absorb in the far-red region of the solar spectrum thereby extending the spectral range of photosynthetically active radiation 1,2. The synthesis and introduction of these far-red Chls into the photosynthetic apparatus of plants might improve the efficiency of oxygenic photosynthesis, especially in far-red enriched environments, such as in the lower regions of the canopy 3. Production of Chl f requires the ChlF subunit, also known as PsbA4 4 or super-rogue D1 5 , a paralog of the D1 subunit of photosystem II (PSII) which together with D2 binds co-factors involved in the light-driven oxidation of water. Current ideas suggest that ChlF oxidizes Chl a to Chl f in a homodimeric ChlF reaction center (RC) complex and represents a missing link in the evolution of the heterodimeric D1/D2 RC of PSII 4,6. However, unambiguous biochemical support for this proposal is lacking. Here we show that ChlF can substitute for D1 to form modified PSII complexes capable of producing Chl f. Remarkably mutation of just two residues in D1 converts oxygenevolving PSII into a Chl f synthase. Overall, we have identified a new class of PSII

Photosystem II (PSII) is the multi-subunit light-driven oxidoreductase that drives photosynthetic electron transport using electrons extracted from water. To investigate the initial steps of PSII assembly, we used strains of the cyanobacterium Synechocystis sp. PCC 6803 arrested at early stages of PSII biogenesis and expressing affinity-tagged PSII subunits to isolate PSII reaction center assembly (RCII) complexes and their precursor D1 and D2 modules (D1mod and D2mod). RCII preparations isolated using either a His-tagged D2 or a FLAG-tagged PsbI subunit contained the previously described RCIIa and RCII* complexes that differ with respect to the presence of the Ycf39 assembly factor and high-light-inducible proteins (Hlips) and a larger complex consisting of RCIIa bound to monomeric PSI. All RCII complexes contained the PSII subunits D1, D2, PsbI, PsbE, and PsbF and the assembly factors rubredoxin A (RubA) and Ycf48, but we also detected PsbN, Slr1470, and the Slr0575 proteins, which all have plant homologs. The RCII preparations also contained prohibitins/stomatins (Phbs) of unknown function and FtsH protease subunits. RCII complexes were active in light-induced primary charge separation and bound chlorophylls, pheophytins, beta-carotenes, and heme. The isolated D1mod consisted of D1/PsbI/Ycf48 with some Ycf39 and Phb3, while D2mod contained D2/cytochrome b559 with co-purifying PsbY, Phb1, Phb3, FtsH2/FtsH3, CyanoP, and Slr1470. As stably bound chlorophyll was detected in D1mod but not D2mod, formation of RCII appears to be important for stable binding of most of the chlorophylls and both pheophytins. We suggest that chlorophyll can be delivered to RCII from either monomeric PSI or Ycf39/Hlip complexes.

Photosystem II is the water-oxidizing and O2-evolving enzyme of photosynthesis. How and when this remarkable enzyme arose are fundamental questions in the history of life that have remained difficult to answer. Here, recent advances in our understanding of the origin and evolution of photosystem II are reviewed and discussed in detail. The evolution of photosystem II indicates that water oxidation originated early in the history of life, long before the diversification of cyanobacteria and other major groups of prokaryotes, challenging and transforming current paradigms on the evolution of photosynthesis. We show that photosystem II has remained virtually unchanged for billions of years, and yet the nonstop duplication process of the D1 subunit of photosystem II, which controls photochemistry and catalysis, has enabled the enzyme to become adaptable to variable environmental conditions and even to innovate enzymatic functions beyond water oxidation. We suggest that this evolvability can be harnessed to develop novel light-powered enzymes with the capacity to carry out complex multistep oxidative transformations for sustainable biocatalysis. Expected final online publication date for the Annual Review of Plant Biology, Volume 74 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Aflatoxin-B1 (AFB1) is a common contaminant for staple foods during the storage process. Chronic exposure to AFB1 is widely known to induce the development of hepatocellular carcinoma (HCC). However, there is a lack of understanding of AFBi role in HCC mechanism. This research aims to identify protein(s) in HCC that might interact with AFB1 and to predict the pathway effected by AFB1. Analyses were performed using bioinformatics tools. SMILES notation of AFB1 was submitted into Swiss Target Prediction. Interaction among predicted proteins were analyzed by using STRING. The 3D structure of target protein was constructed by homology modeling. Reverse docking was performed, and the result was ranked based on binding affinity score. Furthermore, protein interaction network was constructed and analyzed by using Cytoscape. Results showed that three protein groups were predicted as target of AFB1, such as kinases, phosphatases, and G protein-coupled receptor with probability of 46.7%, 20%, and 6.7%, respectively. Seven proteins of kinases were strongly related to HCC, including RAF1, MAPK1, MAPK3, AKT1, EGFR, GSK3B, and mTOR. Reverse docking considered the AKT1-AFB1 as the most potential complex with the lowest affinity score -10.2 kcal.mol-1. It has hydrophobic bonds in Trp80, Val270, Tyr272, Asp292, Thr211, Leu210, Leu264, and Lys268 residues, whereas hydrogen bond in Ser205 residues. Moreover, further analysis demonstrated that interaction of AKT1-AFB1 is related to the metastasis pathway in HCC mechanism.