Organization of protein complexes and a mechanism for grana formation in photosynthetic membranes as revealed by cryo‐electron microscopy

Abstract

Plant and algal chloroplasts and their ultrastructure were one of the first specimens to be studied by microscopy, and their granular nature was first described by Van Leeuwenhoek in 1676. Here we have used cryo-electron tomography and three-dimensional reconstruction to resolve chloroplast ultrastructure at a level where individual protein complexes can be observed. The data reveal features of the ultrastructure which are consistent with a simple hypothesis for the generation of the characteristic stacked grana described by Leeuwenhoek. We find that stacked regions can be formed by invaginations of the 'sac-like' structure of the membrane. Two, or more, invaginations associate together to give stacks of membranes within the sac. In the tomograms, both the stacked and unstacked regions of the membrane display lateral heterogeneity in terms of the particles embedded in them. Unstacked regions display microdomains that are densely packed with CF 1 -CF 0 proton ATPases that predominantly occupy parts where the diskshaped sacs curve at the periphery. Stacked regions display membranes packed with photosystem II complexes.

A Biomimetic-Computational Approach to Optimizing the Quantum Efficiency of Photovoltaics

“…With respect to LHCII one should take into account positioning LHCII next to PSII as well as in a separate, complementary membrane thus permitting to test for both, horizontal (intramembrane) and vertical (intermembrane) energy transfer, respectively. The presence of LHCII in a membrane different from PSII is supported by strong biochemical evidence and tomographic data [3], and it has also been noted that the organization of LHCII may change in response to environmental conditions [9][10][11].Theoretical investigations thus far have focused on UV-Vis spectra calculations for single Chla, Chlb, the strong coupling special Chla/Chla pair (D1/D2, the reaction center) and intermediate coupling Chlb/Chlb pairs in LHCII. As expected, the TD-DFT ωB97X-D [12] calculated spectra showed strong communication (strong red-shift) between the Chla/Chla pair that has a short MgMg distance (8 Å) and varying degrees of weaker communication (little to no red-shift) for Chlb/Chlb pairs in the LHCII displaying Mg-Mg distances above 9 Å.…”

“…With respect to LHCII one should take into account positioning LHCII next to PSII as well as in a separate, complementary membrane thus permitting to test for both, horizontal (intramembrane) and vertical (intermembrane) energy transfer, respectively. The presence of LHCII in a membrane different from PSII is supported by strong biochemical evidence and tomographic data [3], and it has also been noted that the organization of LHCII may change in response to environmental conditions [9][10][11].…”

Small-Angle X-Ray and Neutron Scattering on Photosynthetic Membranes

“…1-200 nm in near in vivo conditions and is widely applied in structural biology and soft matter sciences. Small-angle scattering complements various microscopic techniques, such as TEM (Menke, 1960;Paolillo and Paolillo, 1970;Staehelin, 1986;Austin and Staehelin, 2011;Armbruster et al, 2013;Heinz et al, 2016;Kowalewska et al, 2016;Wood et al, 2018;Kowalewska et al, 2019;Wood et al, 2019;Li et al, 2020), scanning electron microscopy (Mustárdy and Jánossy, 1979;Armbruster et al, 2013), cryo-EM (Ford et al, 2002;Kirchhoff et al, 2011;Engel et al, 2015), cryoelectron tomography (Shimoni et al, 2005;Austin and Staehelin, 2011;Daum and Kühlbrandt, 2011;Kouřil et al, 2011;Ford and Holzenburg, 2014;Bussi et al, 2019;Rast et al, 2019), atomic force microscopy (Kaftan et al, 2002;Sturgis et al, 2009;Sznee et al, 2011;Grzyb et al, 2013;Onoa et al, 2014), confocal laser scanning microscopy (Kowalewska et al, 2016;Mazur et al, 2019), and live cell imaging (Iwai et al, 2014;Iwai et al, 2016). The first scattering studies on photosynthetic membranes were performed in 1953 by Finean et al (1953) and has continued ever since.…”