| Increased focus on the development of artificial photosynthetic systems and alternative energy sources has led to interest in how photosynthetic organisms adapt to stressful environmental conditions. Plants, algae, and cyanobacteria are particularly sensitive to high light intensity. Although repair mechanisms are in place to prevent long-term damage and inhibition from light stress, signals for initiation of key steps in repair are largely unknown. Post-translational modifications (PTMs) of amino acids have been proposed to participate in the signaling pathways. This thesis describes the identification and functional characterization of an oxidative PTM of tryptophan to N-formylkynurenine (NFK) in the Photosystem II (PSII) enzyme. PSII catalyzes the photo-induced water oxidation reaction in oxygenic photosynthesis. In vitro and in vivo biochemical studies suggest that NFK plays a role in protecting PSII from light-induced stress and functions as a signal in repair. This work has led to a new model of the signal and repair process. Preliminary work on 2D crystallization of an intact plant PSII complex is also presented. These experiments show promise for on-going structural studies by electron crystallography. PSII structure determination under native and light-stressed conditions may provide insight into conformational and sub-complex composition changes that accompany light stress and repair. |
