Structure and function of intact photosystem 1 monomers from the cyanobacterium Thermosynechococcus elongatus

Structure and Function of Photosynthetic Reaction Centres

Extensive biochemical, biophysical, molecular biological and structural studies on a wide range of prokaryotic and eukaryotic photosynthetic organisms has revealed common features of their reaction centres where light induced charge separation and stabilization occurs. There is little doubt that all reaction centres have evolved from a common ancestor and have been optimized to maximum efficiency. As such they provide principles that can be used as a blueprint for developing artificial photo-electrochemical catalytic systems to generate solar fuels. This chapter summarises the common features of the organization of cofactors, electron transfer pathways and protein environments of reaction centres of anoxygenic and oxygenic phototrophs. In particular, the latest molecular details derived from X-ray crystallography are discussed in context of the specific catalytic functions of the Type I and Type II reaction centres.

Lifetimes of photosystem I and II proteins in the cyanobacterium Synechocystis sp. PCC 6803

The half-life times of photosystem I and II proteins were determined using (15)N-labeling and mass spectrometry. The half-life times (30-75h for photosystem I components and <1-11h for the large photosystem II proteins) were similar when proteins were isolated from monomeric vs. oligomeric complexes on Blue-Native gels, suggesting that the two forms of both photosystems can interchange on a timescale of <1h or that only one form of each photosystem exists in thylakoids in vivo. The half-life times of proteins associated with either photosystem generally were unaffected by the absence of Small Cab-like proteins.

NdhP and NdhQ: two novel small subunits of the cyanobacterial NDH-1 complex

The subunit composition of the NAD(P)H dehydrogenase complex of Thermosynechococcus elongatus was analyzed by different types of mass spectrometry. All 15 known subunits (NdhA-NdhO) were identified in the purified NDH-1L complex. Moreover, two additional intact mass tags of 4902.7 and 4710.5 Da could be assigned after reannotation of the T. elongatus genome. NdhP and NdhQ are predicted to contain a single transmembrane helix each, and homologues are apparent in other cyanobacteria. Additionally, ndhP is present in some cyanophages in a cluster of PSI genes and exhibits partial similarity to NDF6, a subunit of the plant NDH-1 complex.

Manganese limitation induces changes in the activity and in the organization of photosynthetic complexes in the cyanobacterium Synechocystis sp. strain PCC 6803

Manganese (Mn) ions are essential for oxygen evolution activity in photoautotrophs. In this paper, we demonstrate the dynamic response of the photosynthetic apparatus to changes in Mn bioavailability in cyanobacteria. Cultures of the cyanobacterium Synechocystis PCC 6803 could grow on Mn concentrations as low as 100 nm without any observable effect on their physiology. Below this threshold, a decline in the photochemical activity of photosystem II (PSII) occurred, as evident by lower oxygen evolution rates, lower maximal photosynthetic yield of PSII values, and faster Q(A) reoxidation rates. In 77 K chlorophyll fluorescence spectroscopy, a peak at 682 nm was observed. After ruling out the contribution of phycobilisome and iron stress-induced IsiA proteins, this band was attributed to the accumulation of partially assembled PSII. Surprisingly, the increase in the 682-nm peak was paralleled by a decrease in the 720-nm peak, dominated by PSI fluorescence. The effect on PSI was confirmed by measurements of the P(700) photochemical activity. The loss of activity was the result of two processes: loss of PSI core proteins and changes in the organization of PSI complexes. Blue native-polyacrylamide gel electrophoresis analysis revealed a Mn limitation-dependent dissociation of PSI trimers into monomers. The sensitive range for changes in the organization of the photosynthetic apparatus overlaps with the range of Mn concentrations measured in natural environments. We suggest that the ability to manipulate PSI content and organization allows cyanobacteria to balance electron transport rates between the photosystems. At naturally occurring Mn concentrations, such a mechanism will provide important protection against light-induced damage.