Cyanobacteria photosystems

Biesiadka, J., Loll, B., Kern, J., Irrgang K/D. and Zouni, A. (2004). Crystal structure of cyanobacteria photosystem II at 3.2A resolution. Phys. Chem. Chem. Phys., 6, 4733-4736 Canfield, D.E., Habicht, K.S. and Thamdrup, B. (2000). The Achaean sulfur cycle and the early history of atmospheric oxygen. Science, 288, 658-661... 

Fig. 9. (A) EPR spectra of the PS-1 core complex [P700 FeS-X] (a), the complex in which FeS-X was removed (b), and the reconstituted complex (c) (B) Flash-induced absorbance changes monitored at 698 nm for samples (a), (b) and (c) in (A) and their decay kinetics. Figure source Parrett, Mehari and Golbeck (1990) Resolution and reconstitution of the cyanobacteria photosystem I complex. Biochim Biophys Acta 1015 348, 349...

AR HoIzwarth, G Schatz, H Brock and E Bittermann (1993) Energy transfer and charge separation kinetics in photosystem I. Part 1. Picosecond transient absorption and fluorescence study of cyanobacteria photosystem I particles. Biophys J 64 1813-1826... 

All photosynthetic cells contain some form of photosystem. Photosynthetic bacteria, unlike cyanobacteria and eukaryotic phototrophs, have only one photosystem. Interestingly, bacterial photosystems resemble eukaryotic PSII more than PSI, even though photosynthetic bacteria lack Og-evolving capacity. 

Clusters Fa and Fb of photosystem I from cyanobacteria and chloro-plasts are distinguished by their EPR signatures (26, 27) and their reduction potentials (-520 mV for Fa and -580 mV for Fb Ref. (28). The assignment of cysteines in the primary sequence as ligands to individual clusters has been achieved by site-specific mutagenesis (29, Fig. 3), and structural information with regard to the environment of both clusters has been obtained by NMR (24). 

Unlike the photosynthetic apparatus of photosynthetic bacteria, that of cyanobacteria consits of two photosystems, PS I and II, connected by an electron transport chain. The only chlorophyll present is chlorophyll a, and, therefore, chlorophylls b—d are not of interest in this article. Chlorophyll a is the principal constituent of PS I. Twenty per cent of isolated pigment-protein complexes contain one P700 per 20—30 chlorophyll a molecules the other 80% contain only chlorophyll a20). The physical and chemical properties of chlorophyll a and its role in photosynthesis have recently been described by Meeks77), Mauzerall75), Hoch60), Butler10), and other authors of the Encyclopedia of Plant Physiology NS Vol. 5. 

Photosystem I is a membrane pigment-protein complex in green plants, algae as well as cyanobacteria, and undergoes redox reactions by using the electrons transferred from photosystem II (PS II) [1], These membrane proteins are considered to be especially interesting in the study of monomolecular assemblies, because their structure contains hydrophilic area that can interact with the subphase as well as hydrophobic domains that can interact either with each other or with detergent and lipids [2], Moreover, studies with such proteins directly at the air-water interface are expected to be a valuable approach for their two-dimensional crystallization. 

The water-plastoquinone photo-oxidoreductase, also known as photosystem II (PSII), embedded in the thylakoid membrane of plants, algae and cyanobacteria, uses solar energy to power the oxidation of water to dioxygen by a special centre containing four Mn ions. The overall reaction catalysed by PSII is outlined below ... 

In this system, oxygen is produced by photosystem II, as in green plants and cyanobacteria. The photosynthetic electron transfer, via photosystem I, is linked by low-potential electron carriers to hydrogenase, which produces H2 (Fig. 10.3). Benemann and Weare (1974) then went on to investigate H2 evolution by N2-fixing cyanobacterial cultures as a whole-cell source of hydrogen energy. 

Figure 10.3 Z-scheme of oxygenic photosynthesis in green algae and cyanobacteria, showing links to hydrogenase. Q (plastoquinone) and X (an iron-sulfur cluster) are electron acceptors from photosystems II and I, respectively.The two hydrogenases shown are the NADP-dependent bidirectional hydrogenase and a ferredoxin-dependent enzyme.

In plants, algae and cyanobacteria the light-induced charge separation of photosynthesis occurs in 2 large membrane proteins, called photosystem (PS) I and II. PS I catalyzes the ET from plastocyanin (or cytochrome c6) on the luminal side to ferrodoxin (or flavodoxin) on the stromal side of the membrane (for review see reference 177). PS I from the cyanobacterium Thermo(Y13)synechococcus (T.) elongatus was crystallized and an X-ray crystallographic structure at 2.5 A resolution has recently been obtained.18,178 Very recently, the structure from plant PS I has also been reported with a resolution of 4.4 A.179... 

Photosynthetic bacteria have relatively simple phototransduction machinery, with one of two general types of reaction center. One type (found in purple bacteria) passes electrons through pheophytin (chlorophyll lacking the central Mg2+ ion) to a quinone. The other (in green sulfur bacteria) passes electrons through a quinone to an iron-sulfur center. Cyanobacteria and plants have two photosystems (PSI, PSII), one of each type, acting in tandem. Biochemical and biophysical... 

These two reaction centers in plants act in tandem to catalyze the light-driven movement of electrons from HaO to NADP+ (Fig. 19-49). Electrons are carried between the two photosystems by the soluble protein plastocyanin, a one-electron carrier functionally similar to cytochrome c of mitochondria. To replace the electrons that move from PSII through PSI to NADP+, cyanobacteria and plants oxidize H20 (as green sulfur... 

Fig. 3 Schematic model of light-harvesting compartments in photosynthetic organisms and their position with respect to the membrane and the reaction centers. RC1(2) Photosystem I(II) reaction centre. Peripheral membrane antennas Chlorosome/FMO in green sulfur and nonsulfur bacteria, phycobilisome (PBS) in cyanobacteria and rhodophytes and peridinin-chlorophyll proteins (PCP) in dyno-phytes. Integral membrane accessory antennas LH2 in purple bacteria, LHC family in all eukaryotes. Integral membrane core antennas B808-867 complex in green nonsulfur bacteria, LH1 in purple bacteria, CP43/CP47 (not shown) in cyanobacteria and all eukaryotes.

An elegant example of this is the monitoring of herbicide residues via the photosynthetic electron transport (PET) pathway by utilising cyanobacteria or thylakoid membranes (5). For many herbicides the mode of action is as inhibitors of PET, often acting between the 2 photosystems as indicated in figure 3, and the result is a decrease in the photocurrent. 

Karapetyan, N.V., Holzwarth, A.R., and Rogner, M. (1999) The photosystem I trimer of cyanobacteria molecular organization, excitation dynamics and physiological significance, FEBSLetters 460, 395-400. 

Iodolabeling studies on photosystem II particles from higher plants and cyanobacteria (221) and on a PSII complex (227) specifically labeled the herbicide-binding protein. As 1 is believed to donate electrons to Z, the secondary electron donor which is believed to accept electrons from the photosynthetic manganese complex, these experiments indicate a role for this protein on the oxidizing side of PSII. Consequently, Z must at least be located near, if not in, the herbicidebinding polypeptide (222). 

Phycobilins 500 Covalently bound to proteins on the outer surface of photosynthetic membranes in cyanobacteria and red algae serve in light-harvesting antennae of Photosystem II... 

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