Atomic Force Microscopy Captures Light-Induced Higher-Order Structural Dynamics in Photosystem II Supercomplexes

Area of Science:

• Plant Biology
• Photosynthesis Research
• Molecular Biophysics

Background:

• Photosystem II (PSII)-light-harvesting complex II (LHCII) supercomplexes are crucial for photosynthesis in plant thylakoid membranes.
• These supercomplexes form higher-order structures influenced by environmental light conditions.

Purpose of the Study:

• To visualize PSII-LHCII supercomplex organization in isolated thylakoid membranes using high-speed atomic force microscopy (AFM).
• To investigate the impact of high-light acclimation on the supramolecular organization of PSII-LHCII assemblies.
• To determine the role of the PsbS protein in regulating PSII-LHCII organization under high light.

Main Methods:

• High-speed atomic force microscopy (AFM) for visualizing isolated thylakoid membranes.
• Biochemical analyses to complement AFM imaging.
• Three-dimensional (3D) PSII model fitting for detailed structural analysis.

Main Results:

• AFM revealed disrupted semicrystalline-array-like PSII-LHCII assemblies under high-light acclimation.
• Two configurations of semicrystalline arrays were identified: parallel and offset.
• The offset array configuration was destabilized under high-light acclimation in a PsbS-dependent manner, while the parallel array remained stable.

Conclusions:

• High-light acclimation significantly alters the organization of PSII-LHCII supercomplexes in plant thylakoid membranes.
• PsbS plays a critical role in stabilizing PSII-LHCII supercomplex organization, particularly the offset array, under high-light conditions.