High-resolution model of Arabidopsis Photosystem II reveals the consequences of digitonin-extraction

Abstract

In higher plants, the photosynthetic process is performed and regulated by Photosystem II (PSII). Arabidopsis thaliana was the first higher plant with a fully sequenced genome, conferring it the status of a model organism; nonetheless, a high-resolution structure of its Photosystem II is missing. We present the first Cryo-EM high-resolution structure of Arabidopsis PSII supercomplex with average resolution of 2.79 Å, an important model for future PSII studies. The digitonin extracted PSII complexes demonstrate the importance of: the LHG2630-lipid-headgroup in the trimerization of the light-harvesting complex II; the stabilization of the PsbJ subunit and the CP43-loop E by DGD520-lipid; the choice of detergent to maintain the integrity of membrane protein complexes. We propose that PsbW and PsbH subunits participate in the phospho-signalling dimerization of the complex, important to the assembly/repair processes of Photosystem II. Furthermore, our data shows at the anticipated Mn4CaO5-site a single metal ion density as a reminiscent early stage of PSII photoactivation.

Molecular Evolution of Far-Red Light-Acclimated Photosystem II

“…The homology models cannot capture the positions of most of the N-terminal residues that comprise the FRL-specific extension of FRL-PsbH or that of its ancestral sequence, and even the residues that can be modeled in the N-terminal regions are likely positioned with low confidence, but the FRLspecific N-terminal extensions could alter the region of the SQD and/or the other interactions at the dimerization interface. Furthermore, it was surprising that the apo-FRL-PSII structure lacked FRL-PsbH, as PsbH is found in all other cryo-EM structures of PSII, even assembly intermediate-like-, apo-, and monomeric-PSII complexes [54][55][56][57]. These observations suggest that FRL-PsbH binds less tightly to the FRL-PSII complex relative to VL-PsbH, which could have implications for details of assembly and repair.…”