Life on Earth depends on photosynthesis, the conversion of light energy from the Sun to chemical energy. In plants, green algae and cyanobacteria, this process is driven by the cooperation of two large protein-cofactor complexes, photosystems I and II, which are located in the thylakoid photosynthetic membranes. The crystal structure of photosystem I from the thermophilic cyanobacterium Synechococcus elongatus described here provides a picture at atomic detail of 12 protein subunits and 127 cofactors comprising 96 chlorophylls, 2 phylloquinones, 3 Fe4S4 clusters, 22 carotenoids, 4 lipids, a putative Ca2+ ion and 201 water molecules. The structural information on the proteins and cofactors and their interactions provides a basis for understanding how the high efficiency of photosystem I in light capturing and electron transfer is achieved.

Three-dimensional structure of cyanobacterial photosystem I at 2.5 Å resolution

Communication modules in bacterial signaling proteins.

The manganese and calcium ions of photosynthetic oxygen evolution.

Energy transfer and trapping in photosynthesis

Protein phosphorylation in regulation of photosynthesis

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2893%2980831-E

PsaL subunit is required for the formation of photosystem I trimers in the cyanobacterium Synechocystis sp. PCC 6803

▪ Abstract Photosystem I is the light-driven plastocyanin-ferredoxin oxidoreductase in the thylakoid membranes of cyanobacteria and chloroplasts. In recent years, sophisticated spectroscopy, molecular genetics, and biochemistry have been used to understand the light conversion and electron transport functions of photosystem I. The light-harvesting complexes and internal antenna of photosystem I absorb photons and transfer the excitation energy to P700, the primary electron donor. The subsequent charge separation and electron transport leads to the reduction of ferredoxin. The photosystem I proteins are responsible for the precise arrangement of cofactors and determine redox properties of the electron transfer centers. With the availability of genomic information and the structure of photosystem I, one can now probe the functions of photosystem I proteins and cofactors. The strong reductant produced by photosystem I has a central role in chloroplast metabolism, and thus photosystem I has a critical role in...

PHOTOSYSTEM I: Function and Physiology

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I I. GENETIC AND PHYSIOLOGICAL CHARACTERIZATION OF PHYLLOQUINONE BIOSYNTHETIC PATHWAY MUTANTS IN SYNECHOCYSTIS SP. PCC 6803

The precursor for a Lemna light-harvesting chlorophyll a/b protein (pLHCP) has been synthesized in vitro from a single member of the nuclear LHCP multigene family. We report the sequence of this gene. When incubated with Lemna chloroplasts, the pLHCP is imported and processed into several polypeptides, and the mature form is assembled into the light-harvesting complex of photosystem II (LHC II). The accumulation of the processed LHCP is enhanced by the addition to the chloroplasts of a precursor and a co-factor for chlorophyll biosynthesis. Using a model for the arrangement of the mature polypeptide in the thylakoid membrane as a guide, we have created mutations that lie within the mature coding region. We have studied the processing, the integration into thylakoid membranes, and the assembly into light-harvesting complexes of six of these deletions. Four different mutant LHCPs are found as processed proteins in the thylakoid membrane, but only one appears to have an orientation in the membrane that is similar to that of the wild type. No mutant LHCP appears in LHC II. The other two mutant LHCPs cannot be detected within the chloroplasts. We conclude that stable complex formation is not required for the processing and insertion of altered LHCPs into the thylakoid membrane. We discuss the results in light of our model.

/pdf/functional-and-mutational-analysis-of-the-light-harvesting-1jgb0n2avn.pdf

Functional and mutational analysis of the light-harvesting chlorophyll a/b protein of thylakoid membranes.

As a first step in establishing a proteome database for maize, we have embarked on the identification of the leaf proteins resolved on two-dimensional (2-D) gels. We detected nearly 900 spots on the gels with a pH 4-7 gradient and over 200 spots on the gels with a pH 6-11 gradient when the proteins were visualized with colloidal Coomassie blue. Peptide mass fingerprints for 300 protein spots were obtained with matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometer and 149 protein spots were identified using the protein databases. We also searched the pdbEST databases to identify the leaf proteins and verified 66% of the protein spots that had been identified using the protein databases. Sixty-seven additional protein spots were identified from expressed sequence tags (ESTs). Many abundant leaf proteins are present in multiple spots. Functions of over 50% of the abundant leaf proteins are either unknown or hypothetical. Our results show that EST databases in conjunction with peptide mass fingerprints can be used for identifying proteins from organisms with incomplete genome sequence information.

Parag R. Chitnis

Papers

PsaL subunit is required for the formation of photosystem I trimers in the cyanobacterium Synechocystis sp. PCC 6803

PHOTOSYSTEM I: Function and Physiology

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I I. GENETIC AND PHYSIOLOGICAL CHARACTERIZATION OF PHYLLOQUINONE BIOSYNTHETIC PATHWAY MUTANTS IN SYNECHOCYSTIS SP. PCC 6803

Functional and mutational analysis of the light-harvesting chlorophyll a/b protein of thylakoid membranes.

The proteome of maize leaves: use of gene sequences and expressed sequence tag data for identification of proteins with peptide mass fingerprints.