Subunit PsaE

The structure of subunit PsaE (8 kDa) in solution was determined by 1H and 15N NMR spectroscopy 34 . It shows a compact structure of five anti-parallel stranded -sheets. The core structure of PsaE, consisting of five a-strands is essentially the same in solution and in PsaE attached to the PSI complex. The main difference between the free and bound PsaE are the conformations of the loops and the C-and N-terminus. The flexible loop connecting the P-sheets P3 (C) and P4 (D) was not well resolved...

Interaction with Electron Donors and Acceptors

The binding mode of ferredoxin and ferredoxin-NADP-reductase (FNR) to plant PSI is not clear. A relatively strong interaction between the two proteins was demonstrated -45, 46 and a crystal structure of the ferredoxin-FNR complex has been determined 47 . It has been reported that FNR in higher plant chloroplasts is localized peripherally on the stromal side of thylakoid membranes through association with a membrane-intrinsic protein 48, 49 -either cytochrome (cyt) b6f complex 50-52 , NAD(P)H...

Early Spectroscopic Results from Chloroplast Membranes

Determining the structure of the OEC has been the target of a large number of researchers, exploiting every applicable spectroscopic probe. Two spectroscopic techniques have historically provided the most significant results electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS). In EPR spectroscopy, a magnetic field splits the energy levels of paramagnetic electron states and spin transitions are driven using microwave radiation. The results obtained can...

Structure and Function of CF0F1

H+-ATP synthases have three catalytic nucleotide binding sites on the P-subunits and three non-catalytic nucleotide binding sites on the a-subunits they use a remarkable mechanism to synthesize, or to hydrolyze, ATP (binding change mechanism 64, 66 ). According to this mechanism, the catalytic sites work cooperatively. At a given time, each site has a different conformation. For example, site 1 is in an open conformation and can bind substrates site 2 is in a closed conformation, it does not...

Subunits PsaF PsaJ and PsaX

Of these subunits (Figure 2.2d) exposed to the lipid bilayer of the membrane, PsaF and PsaJ are located at positions which are roughly related by the pseudo-C2 axis of PsaA PsaB to PsaL and PsaI (Figure 2.1c). PsaF, PsaJ, and PsaX contain a single transmembrane a-helix each, but PsaF, the largest of these subunits, has the most unusual structure of the small membrane-integral subunits of PSI. It consists of two domains an N-terminal domain at the lumenal side and a C-terminal domain which is...

The Role of LHCII in Nonphotochemical Quenching

In the light reaction of photosynthesis, the consumption of excitation energy to trigger charge separation in the reaction center will lead to a decrease of chlorophyll fluorescence quantum yield, a phenomenon termed photochemical quenching. When the light intensity exceeds the photosynthetic capacity, the excess excitation energy has to be dissipated non-radiatively as heat so that its potential damaging effects can be avoided. The non-radiative dissipation (NRD) can be detected as...

The XRay Crystal Structure of the LH2 Complex from Rps acidophila strain 10050

In 1995, the X-ray crystal structure of the LH2 complex from Rps. acidophila strain 10050 was first resolved at 2.5A 11 . This has subsequently been improved to 2A 12 . Figure 14.2 shows the overall structure of LH2. It is a circular nonamer composed of nine pairs of a,P-dimers. As predicted, before the crystal structure was determined, each apoprotein contains a single transmembrane spanning a - helix. Looking down on the top of the complex, in a direction that would be equivalent to looking...

Bacteriochlorophyll Dimer

All photosynthetic complexes have bacteriochlorophyll or chlorophyll cofactors that are the focal point for light excitation and serve as the primary electron donor. Figure 12.3 a Structure of the bacteriochlorophyll dimer from R. sphaeroides and some surrounding amino acid residues, including His L173 and M202 that each coordinate one of the Mg, His L168 that is hydrogen bonded to the acetyl group of ring A on one side, and Leu L131, Leu M160, and Phe M197, that, when changed to histidines,...

The Structure of RCLH1 Core Complexes

Over the past few years there, there have been several detailed investigations into the structure of the RC-LH1 core complexes from a range of different species of purple bacteria. This is a unified view of their structure. Please note, however, that, because there is no high resolution structure of a purple bacterial core complex, this view may change in the future. It appears that there are two types of core complexes -3 . Some species, such as Rps. viridis 24 , or Rps. palustris 25 , have...