The light-harvesting complex of photosystem II (LHCII) is the main site of light absorption and energy transfer by pigment molecules during photosynthesis in higher plants and green algae. LHCII also functions as a photoprotection site when the plant is exposed to intense light conditions. Overall, this project aims to capture the structural dynamics of LHCII throughout the process of photosynthesis to further understand how it regulates the absorption and utilization of photons, especially in intense light conditions. The LHCII protein samples were extracted from Spinacia oleracea (spinach) and crystallized using sitting drop vapor diffusion under dark conditions. Green hexagonal crystals, with sizes ranging from 30 to 100 microns, were harvested after two days. Ultrafast X-ray free-electron lasers (XFEL) in SACLA Japan and LCLS Stanford with the Drop-on-Tape sample delivery setup were used to collect time-resolved X-ray diffraction data. Here, we report room-temperature crystal structures of LHCII in the dark and illuminated states. An aspect we are looking at is the B-factor changes between the two states that may provide insights into the mobility and flexibility of LHCII, which can indicate physiological conformational changes during energy absorption and quenching. Further time-resolved measurements may reveal details of photo-induced structural changes in LHCII, particularly those that occur around the pigment molecules.
Nangca et al. (Sun,) studied this question.