Functional architecture of higher plant photosystem II supercomplexes

Photosystem II (PSII) is a large multiprotein complex, which catalyses water splitting and plastoquinone reduction necessary to transform sunlight into chemical energy. Detailed functional and structural studies of the complex from higher plants have been hampered by the impossibility to purify it to homogeneity. In this work, homogeneous preparations ranging from a newly identified particle composed by a monomeric core and antenna proteins to the largest C2S2M2 supercomplex were isolated. Characterization by biochemical methods and single particle electron microscopy allowed to relate for the first time the supramolecular organization to the protein content. A projection map of C2S2M2 at 12 Å resolution was obtained, which allowed determining the location and the orientation of the antenna proteins. Comparison of the supercomplexes obtained from WT and Lhcb-deficient plants reveals the importance of the individual subunits for the supramolecular organization. The functional implications of these findings are discussed and allow redefining previous suggestions on PSII energy transfer, assembly, photoinhibition, state transition and non-photochemical quenching

The peripheral light-harvesting complexes from purple sulfur bacteria have different 'ring' sizes

AbstractThe integral membrane light-harvesting (LH) proteins from purple photosynthetic bacteria form circular oligomers of an elementary unit that is composed of two very hydrophobic polypeptides, termed α and β. These apoprotein dimers are known to associate into closed circular arrays of 8, 9 and 16 α/β-mers. We report the existence of peripheral LH proteins purified from Allochromatium vinosum with two intermediate ring sizes and postulate that one is a 13 α/β-mer. This shows that LH proteins are able to form membrane rings of continuously increasing diameter from 68 to 115Å. The presence of these new ring sizes warrants further study, as it will help to further validate the structure–function models of LH proteins currently found in the literature

Photosystem II Supercomplexes Of Higher Plants:Isolation And Determination Of The Structural And Functional Organization

Photosystem II is a supercomplex composed of 27-28 different subunits and it represents the most important machinery of the plants photosynthetic appara- tus, having the ability to split water into oxygen, protons and electrons. In the last few years the structures of most of the photosynthetic complexes have been resolved, allowing to organize in a ‘‘visual framework’’ the large body of information obtained by genetics, biochemical and spectroscopic methods about the function and organization of the complexes. Only the struc- ture of PSII-LHCII from higher plants is still lacking due to the impossibility to obtain a homogeneous and stable preparation of the supercomplex, which has also prevented functional and spectroscopic studies.In this work homogeneous and stable Photosystem II supercomplexes with dif- ferent antenna size were isolated. A full gallery of complexes, from the core to the largest C2S2M2, was characterized by electron microscopy and biochemi- cal and spectroscopic methods, allowing to relate for the first time the supramo- lecular organization to the protein and pigment content and the energy transfer processes. A new complex containing a monomeric core, a trimeric LHCII (S) and a monomeric CP26 was isolated, showing that the antenna proteins can bind to the monomeric core in contrast to the current belief. The comparison of the supercomplexes obtained from WT plants and knock out mutants of sev- eral Lhcb proteins allowed determining the hierarchy of the assembly and to suggest a role for the individual subunits. The data also provides information about the organization of the oxygen evolving complex. For the first time it was possible to study the energy transfer process in the supercomplexes with the use of picosecond fluorescence spectroscopy.The functional implication of these results on photoinhibition, state transition and energy transfer are discussed

Photosystem II Supercomplexes Of Higher Plants: Isolation And Determination Of The Structural And Functional Organization

Photosystem II is a supercomplex composed of 27-28 different subunits and it represents the most important machinery of the plants photosynthetic appara- tus, having the ability to split water into oxygen, protons and electrons. In the last few years the structures of most of the photosynthetic complexes have been resolved, allowing to organize in a ‘‘visual framework’’ the large body of information obtained by genetics, biochemical and spectroscopic methods about the function and organization of the complexes. Only the struc- ture of PSII-LHCII from higher plants is still lacking due to the impossibility to obtain a homogeneous and stable preparation of the supercomplex, which has also prevented functional and spectroscopic studies. In this work homogeneous and stable Photosystem II supercomplexes with dif- ferent antenna size were isolated. A full gallery of complexes, from the core to the largest C2S2M2, was characterized by electron microscopy and biochemi- cal and spectroscopic methods, allowing to relate for the first time the supramo- lecular organization to the protein and pigment content and the energy transfer processes. A new complex containing a monomeric core, a trimeric LHCII (S) and a monomeric CP26 was isolated, showing that the antenna proteins can bind to the monomeric core in contrast to the current belief. The comparison of the supercomplexes obtained from WT plants and knock out mutants of sev- eral Lhcb proteins allowed determining the hierarchy of the assembly and to suggest a role for the individual subunits. The data also provides information about the organization of the oxygen evolving complex. For the first time it was possible to study the energy transfer process in the supercomplexes with the use of picosecond fluorescence spectroscopy. The functional implication of these results on photoinhibition, state transition and energy transfer are discussed

The photosystem II light-harvesting protein Lhcb3 affects the macrostructure of photosystem II and the rate of state transitions in Arabidopsis

The main trimeric light-harvesting complex of higher plants (LHCII) consists of three different Lhcb proteins (Lhcb1-3). We show that Arabidopsis thaliana T-DNA knockout plants lacking Lhcb3 (koLhcb3) compensate for the lack of Lhcb3 by producing increased amounts of Lhcb1 and Lhcb2. As in wild-type plants, LHCII-photosystem II (PSII) supercomplexes were present in Lhcb3 knockout plants (koLhcb3), and preservation of the LHCII trimers (M trimers) indicates that the Lhcb3 in M trimers has been replaced by Lhcb1 and/or Lhcb2. However, the rotational position of the M LHCII trimer was altered, suggesting that the Lhcb3 subunit affects the macrostructural arrangement of the LHCII antenna. The absence of Lhcb3 did not result in any significant alteration in PSII efficiency or qE type of nonphotochemical quenching, but the rate of transition from State 1 to State 2 was increased in koLhcb3, although the final extent of state transition was unchanged. The level of phosphorylation of LHCII was increased in the koLhcb3 plants compared with wild-type plants in both State 1 and State 2. The relative increase in phosphorylation upon transition from State 1 to State 2 was also significantly higher in koLhcb3. It is suggested that the main function of Lhcb3 is to modulate the rate of state transitions