Dynamic Regulation of the Form and Function of Photosystem II, a Membrane Protein Complex

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ABSTRACTThis project focuses on understanding the dynamic regulation of the multisubunit pigment protein complex Photosystem II (PSII). Localized in the thylakoid membrane of cyanobacteria, algae and plants, PSII catalyzes light-induced electron transfer from water to plastoquinone with concomitant evolution of oxygen. The life history of PSII is intriguing in that its normal function leads to rapid turnover of this large integral membrane protein complex. This process, undoubtedly carefully orchestrated to maintain critically important water oxidation activities, must require a host of assembly factors, very few of which have been identified to date. Also, oxygenic photosynthetic organisms in general, and cyanobacteria in particular, inhabit almost every ecological niche on the planet, surviving in temperatures from 4 degrees Celsius to 75 degrees Celsius, under widely varying nutritional environs. Recent genome level data suggest that among such organisms, PSII exhibits a high degree of plasticity in both composition and regulation to optimize its function. For example, N2-fixing cyanobacteria such as Cyanothece 51142 are capable of oxygenic photosynthesis and N2 fixation in single cells. These two metabolic processes are at odds with each other, since the N2-fixing enzyme, nitrogenase, is highly sensitive to O2. To resolve this conflict, these organisms have developed a type of temporal regulation in which N2 fixation and photosynthesis occur at different times throughout a diurnal cycle. Again, little is known about how the form and function of PSII are regulated so that every night, PSII becomes inactive.The specific aims of this project are:I. To investigate the dynamic forms of PSII under diverse environmental conditions.A. To examine diurnal regulation of PSII activity in Cyanothece 51142.B. To elucidate the effect of chloride concentration on the composition of the lumenal proteins of PSII in Synechocystis as well as Prochloroccous.II. To examine the assembly intermediates of PSII in Synechocystis 6803.A. To investigate PSII assembly intermediates over a time course.B. To define the functions of various lumenal proteins in PSII biogenesis.C. To elucidate the role of the assembly intermediate operon (aio) in PSII biogenesis.Broader ImpactBy harvesting solar radiation, the PSII complex contributes to nearly half of the biomass and bioenergy production on our planet. A detailed understanding of the dynamic nature PSII is necessary to fully comprehend the mechanism of photosynthetic O2-evolution. This project will encompass a broad genomics based approach to provide a multi-disciplinary training environment for all researchers. The project will also help train a number of undergraduate, graduate and post-doctoral students in the general area of bioenergy. Finally, the on-going tradition of all researchers in this project participating in significant outreach activities will be continued.