Collaborative Research: Elucidating the Influence of Metal Binding on Electronic/Geometric Structure-Function Relationships in Photorespiration

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In this project funded by the Chemistry of Life Processes Program of the Chemistry Division, Professors Kyle M. Lancaster of the Cornell University and Arnold J. Bloom of the University of California Davis evaluate the role of differential metal binding, specifically magnesium versus manganese, on the mechanisms and bioenergetics of photorespiration in which Rubisco, the most prevalent protein on the planet, reacts with oxygen rather than with carbon dioxide. This collaboration between a bioinorganic spectroscopist and a plant physiologist seeks to provide new perspectives on the evolution of photosynthesis and the relationships between plant carbon and nitrogen balances under past, present, and future environmental conditions. Such information is critical for maintaining food quality and ensuring world food security in the coming decades. Professors Lancaster and Bloom disseminate this information through articles in the online Encyclopedia of Earth, workshops at scientific meetings, including some organized by Societies of scientists who are members of groups underrepresented in STEM careers, and by writing and keeping up-to-date printed and online textbooks used by students as well as by American and foreign professionals whose work is related to environmental change. The proposed research involves application of a broad range of spectroscopic, kinetics, and computational techniques to contrast protein structure and plant metabolism when manganese or magnesium binds to the enzymes that catalyze the first three chemical steps in the photorespiratory pathway. The Mn2+-bound forms of Rubisco, malic enzyme, and phosphoglycolate phosphatase are characterized by X-ray crystallography and by electron spin resonance, X-ray absorption, and magnetic circular dichroism spectroscopy. Both isolated, intact chloroplasts as well as purified photorespiratory enzymes are studied. The work with isolated chloroplasts involves ratiometric dye measurements of magnesium and manganese concentrations, optode measurements of O2 and CO2 consumption, and mass spectrometric assessment of photorespiratory products. Work carried out on isolated enzymes involves measurement of electron transfer kinetics from manganese Rubisco during oxygenation of ribulose-1,5-bisphosphate as well as investigation of potential physiologically relevant electron transfer partners. The research tests the hypothesis that photorespiration is not a wasteful process, but one that generates reductant to support the conversion of nitrate and sulfate into amino acids. Therefore, C3 carbon fixation may be much more energy efficient than previously assumed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.