Cryo-electron microscopy structure of the intact photosynthetic light-harvesting antenna-reaction center complex from a green sulfur bacterium

The photosynthetic reaction center complex(RCC)of green sulfur bacteria(GSB)consists of the membrane-imbedded RC core and the peripheric energy transmitting proteins called Fenna–Matthews–Olson(FMO).Functionally,FMO transfers the absorbed energy from a huge peripheral light-harvesting antenna named chlorosome to the RC core where charge separation occurs.In vivo,one RC was found to bind two FMOs,however,the intact structure of RCC as well as the energy transfer mechanism within RCC remain to be clarified.Here we report a structure of intact RCC which contains a RC core and two FMO trimers from a thermophilic green sulfur bacterium Chlorobaculum tepidum at 2.9A resolution by cryo-electron microscopy.The second FMO trimer is attached at the cytoplasmic side asymmetrically relative to the first FMO trimer reported previously.We also observed two new subunits(PscE and PscF)and the N-terminal transmembrane domain of a cytochrome-containing subunit(PscC)in the structure.These two novel subunits possibly function to facilitate the binding of FMOs to RC core and to stabilize the whole complex.A new bacteriochlorophyll(numbered as 816)was identified at the interspace between PscF and PscA-1,causing an asymmetrical energy transfer from the two FMO trimers to RC core.Based on the structure,we propose an energy transfer network within this photosynthetic apparatus.

New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis

So far, many important questions and problems concerning the structure and mechanism of photosynthetic oxygen evolution are still unsolved. On the basis of recent achievements in this field, a new structure model is proposed whereby two H2O molecules bind asymmetrically to two manganese ions (Mn1Ⅱ and Mn4Ⅲ) at the open end of 'C' shaped cluster and keep rather large distance. Two histidine residues coordinate to the other two manganese ions in higher oxi-

33 ku protein associated several polypeptides with nearly the same molecular weight but not the same isoelectric point

The 33 ku protein, prepared from NaCI-treated PSII particles, has shown an single band by SDS-PAGE. After being dialyzed against the low-osmotic medium at 4癈, it has been found that the 33 ku protein degraded into several small fragments. This result suggests that the preparations of 33 ku protein probably contain some latent proteinases. it has also been found, by the 2-D electrophoresis and IEF, that the preparations of 33 ku protein not dialyzed against the low-osmotic medium contain several polypeptides with nearly the same molecular weight but not the same isoelectric point as the 33 ku protein.

Comparative Analysis of the Endosperm Proteins Separated by 2-D Electrophoresis for Two Cultivars of Hybrid Rice （Oryza sativa L,）

Liangyoupeijiu is a two-parental-line, and Shanyou63 is a three-parental-line hybrid rice （Oryza sativa L.）. Although both belong to the indica subspecies, they have obvious differences with respect to morphology, physiology and grain quality. Variations in endosperm protein compositions were studied by comparing the 2-D electrophoresis （2-DE） maps for these two cultivars of hybrid rice. After matrix-assisted laser desorption/ionization time of flight mass spectrometry （MALDI-TOF/MS） analysis, a 21-kDa precursor of 19- kDa globulin was identified as the major storage protein for both cultivars. Some isoforms of peroxiredoxin and seed maturation protein were found to only exist in Shanyou63, whereas aldose reductase and starch granule-bound starch synthase were only detected in Liangyoupeijiu. These data might provide a foundation for further comparative studies of these two cultivars of hybrid rice.

Loss of algal Proton Gradient Regulation 5 increases reactive oxygen species scavenging and H2 evolution

Summary We have identified hpm91, a Chlamydomonas mutant lacking Proton Gradient Regulation5 （PGRS） capable of producing hydrogen （H2） for 25 days with more than 3o-fold yield increase compared to wild type. Thus, hpm91 displays a higher capacity of H2 production than a previously characterized pgr5 mutant. Physiological and biochemical characterization of hpm91 reveal that the prolonged H2 production is due to enhanced stability of PSII, which correlates with increased reactive oxygen species （ROS） scavenging capacity during sulfur depriva- tion. This anti-ROS response appears to protect the photosynthetic electron transport chain from photo- oxidative damage and thereby ensures electron supply to the hydrogenase.

Changes in Thermostability of Photosystem Ⅱ and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll a/b Protein Complexes

We studied the difference in thermostability of photosystem Ⅱ （PSII） and leaf lipid composition between a T-DNA insertion mutant rice （Oryza sativa L.） VG28 and its wild type Zhonghuau. Native green gel and SDS-PAGE electrophoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSII photochemistry （FJ Fm） and oxygen-evolving activity of PSII in leaves significantly decreased with increasing temperature. However, the PSII activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of 16：1t and a marked increase in the content of 18：3 compared with the wild type. The effects of lipid composition and unsaturation of membrane lipids on the thermostability of PSII are discussed.

A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina

Photosystem I(PSI)is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin(or cytochrome c6)and the reduction of ferredoxin.This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor(a special chlorophyll(Chl)pair)and electron acceptors A_(0),A_(1),and three Fe_(4)S_(4) clusters,F_(X),F_(A),and F_(B).Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3Åresolution obtained by single-particle cryo-electron microscopy.The A.marina PSI exists as a trimer with three identical monomers.Surprisingly,the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A_(0) is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures.A novel subunit Psa27 is observed in the A.marina PSI structure.In addition,77 Chls,13α-carotenes,two phylloquinones,three Fe-S clusters,two phosphatidyl glycerols,and one monogalactosyl-diglyceride were identified in each PSI monomer.Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.

Structure of plant photosystem I−light harvesting complex I supercomplex at 2.4Å resolution

Photosystem I(PSI)is one of the two photosystems in photosynthesis,and performs a series of electron transfer reactions leading to the reduction of ferredoxin.In higher plants,PSI is surrounded by four light-harvesting complex I(LHCI)subunits,which harvest and transfer energy efficiently to the PSI core.The crystal structure of PSI-LHCI supercomplex has been analyzed up to 2.6Åresolution,providing much information on the arrangement of proteins and cofactors in this complicated supercomplex.Here we have optimized crystallization conditions,and analyzed the crystal structure of PSI-LHCI at 2.4Åresolution.Our structure showed some shift of the LHCI,especially the Lhca4 subunit,away from the PSI core,suggesting the indirect connection and inefficiency of energy transfer from this Lhca subunit to the PSI core.We identified five new lipids in the structure,most of them are located in the gap region between the Lhca subunits and the PSI core.These lipid molecules may play important roles in binding of the Lhca subunits to the core,as well as in the assembly of the supercomplex.The present results thus provide novel information for the elucidation of the mechanisms for the light-energy harvesting,transfer and assembly of this supercomplex.

Phytochrome controlled, long-day photoperiod-inducible protein in rice leaves

A new protein in the leaves of NK58S and NK58 (Oryza sativa L. subsp. japonica), which can be induced by 10 d-long-day photoperiod (14 h light/d) and cannot be induced by 10 d-short-day photoperiod (10 h light/d), has been found by two-dimensional gel electrophoresis. The protein.whose molecular weight and isoelectric point are 36 ku and pH 5.2 respectively, is found to be controlled by phytochrome as shown by the experiment of red light induction-far red light reversion.The existence of this protein in both NK58S and NK58 reflects that some of the responses of NK58S and NK58 might be similar in response to long-day photoperiod, a mild stress.

Function of terahertz spectra in monitoring the decomposing process of biological macromolecules and in investigating the causes of photoinhibition

Chlorophyll α and β-carotene play an important role in harvesting light energy, which is used to drive photosynthesis in plants. In this study, terahertz(THz) and visible range spectra of chlorophyll α and β-carotene and their changes under light treatment were investigated. The results show that the all THz transmission and absorption spectra of chlorophyll α and β-carotene changed upon light treatment, with the maximum changes at 15 min of illumination indicating the greatest changes of the collective vibrational mode of chlorophyll α and β-carotene. The absorption spectra of chlorophyll α in the visible light region decreased upon light treatment, signifying the degradation of chlorophyll a molecules. It can be inferred from these results that the THz spectra are very sensitive in monitoring the changes of the collective vibrational mode, despite the absence of changes in molecular configuration. The THz spectra can therefore be used to monitor the decomposing process of biological macromolecules; however, visible absorption spectra can only be used to monitor the breakdown extent of biological macromolecules.

Commitment and dedication of a Chinese plant physiologist

Professor Peisong Tang(Pei-sung Tang),born in 1903,is one of the co-founders of the modern Chinese plant physiology.You might be familiar with some of his academic achievements:he is the first one to discover respiratory enzymes(cytochorome oxidase)in plants;he proved that multiple respiratory metabolic pathways and electron transfers exist in the rice;he is the first one to experimentally prove the existence of carbonic anhydrase in plants;together with Prof.Zhuxi Wang,he used thermodynamical method to illustrate the mechanism of intracellular water movement,which later has been referred to as the“Tang-Wang theory of cellular water potential”.You probably also know that he is the first Chinese biologist who published in Nature and Science in 1940s and 1950s.But there is something about him that you will not learn from his over 200 publications:his commitment,as a Chinese,to his country and his people,and his dedication,as a scientist,in pursuing science and truths.