STRUCTURE AND MEMBRANE ORGANIZATION OF PHOTOSYSTEM II IN GREEN PLANTS

TLDR

Photosystem II is a pigment protein complex in thylakoid membranes that harnesses solar energy to split water, and its oligomeric state and subunit organization are key structural features. This chapter reviews PSII’s primary to quaternary structures and the functions of its subunits. In vivo PSII organization is inferred from freeze‑etched and freeze‑fracture images of thylakoid membranes, which reveal oligomeric state and subunit arrangement. Freeze‑etched images resolve PSII complexes at 40–50 Å, revealing localization, heterogeneity, dimensions, and shapes, while higher‑resolution 15–40 Å data from single‑particle imaging and 2‑D electron crystallography provide detailed subunit composition.

Abstract

Photosystem II (PSII) is the pigment protein complex embedded in the thylakoid membrane of higher plants, algae, and cyanobacteria that uses solar energy to drive the photosynthetic water-splitting reaction. This chapter reviews the primary, secondary, tertiary, and quaternary structures of PSII as well as the function of its constituent subunits. The understanding of in vivo organization of PSII is based in part on freeze-etched and freeze-fracture images of thylakoid membranes. These images show a resolution of about 40-50 A and so provide information mainly on the localization, heterogeneity, dimensions, and shapes of membrane-embedded PSII complexes. Higher resolution of about 15-40 A has been obtained from single particle images of isolated PSII complexes of defined and differing subunit composition and from electron crystallography of 2-D crystals. Observations are discussed in terms of the oligomeric state and subunit organization of PSII and its antenna components.