Single particle cryo-EM structure elucidation of a Photosystem II complex mimicking a critical step in photoinhibition
Espy, Carolann Lindsay
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Photosystem II (PSII) is an essential protein in the photosynthetic process that houses the oxygen evolution center, which is responsible for producing most of the oxygen in the atmosphere. In order to better understand PSII and its function, it is important to discern the structure of active PSII and the process of photoinhibition. Photoinhibition occurs when the extrinsic subunits are damaged due to overexposure to light, and are then removed, repaired, and replaced. The removal of these extrinsic subunits could be recreated with the help of a urea wash protocol, which removed subunits PsbO, PsbP, and PsbQ. The method used here to elucidate the structure of urea wash PSII, was electron cryo-microscopy (cryo-EM). Utilizing this method and a gentle purification of the protein, a 3D model of an important step in the repair of ‘photoinhibited’ PSII was obtained. Through testing multiple parameters during image processing, several models were generated with estimated resolutions ranging from 20.74 Å to the best estimated resolution of 9.05 Å (Figure 2).