Projection structure of photosystem II In vivo determined by cryo-electron crystallography

Structural analysis of photosystem II in far‐red‐light‐adapted thylakoid membranes

“…In cryoelectron‐microscopic studies of unstained specimens, single crystals in either the upper or lower membrane would be identical (except for γ), and this prediction fits well with our recent observations that unstained specimens show crystals with γ > 90° with the same frequency as those with γ < 90° (Ford, R.C. and Holzenburg, A., unpublished data; see also [25–27]). The observation that the presence of a crystal in one membrane does not impose crystallinity in the other membrane in the pair is significant for various models of PSII connectivity in grana stacks (cf.…”

“…When observed in the electron microscope, these samples may also infrequently be seen to contain 2D crystals of PSII which, if suitably well ordered, are excellent for the elucidation of PSII structure. These arrays have so far been used for the calculation of 2D projection maps and three‐dimensional (3D) maps of native PSII to various resolution limits up to about 13 Å[2,19–21,25–27]. The viridis‐zb63 mutant of barley ( Hordeum vulgare ), which is used in this study, lacks photosystem I (PSI) but retains a fully intact PSII [28,29].…”

An alternative model for photosystem II/light harvesting complex II in grana membranes based on cryo‐electron microscopy studies

“…3B. This supports the conclusion that the higher plant PSII complex is monomeric in vivo , as suggested previously [14,15,19–21,23] . Clearly, caution must be exercised in a more detailed comparison of the two projection maps especially regarding the identification of transmembrane helices, because in the native PSII structure, additional extrinsic proteins and loops will be superimposed (compare to Figure 4), whereas in the current deposition of the cyanobacterial structure, only the transmembrane regions and two of the extrinsic subunits are defined [12] .…”

“…1c,d) is readily achieved, and two‐dimensionally ordered arrays of PSII/LHCII present in these membranes (Fig. 1e) can be observed [13–21]. Cryoelectron microscopy of such two‐dimensional arrays generated projection and three‐dimensional structures of the PSII/LHCII complex.…”

“…With such complexity, it is understandable that knowledge of the structure of PSII/LHCII proteins has largely come from studies of isolated components of the system [10] or subcomplexes that have been removed from the membrane by detergent extraction [11,12]. However two‐dimensional crystalline arrays of PSII/LHCII have sometimes been observed to form in situ in the grana membranes, and these can be studied using electron crystallography techniques [13–21]. Such native crystals are inevitably smaller than crystals of isolated proteins [10] or purified complexes of proteins [11].…”