C-C bond cleavage and generation in TCA cycle driven by radicals and peroxo-bridge like interaction

Abstract

Tricarboxylic acid (TCA) cycle is one of the most important and common metabolic pathways in different kingdoms of life, in which citrate synthase catalyzes the first irreversible reaction and the rate-limiting step. Reversed oxidative tricarboxylic acid (roTCA) cycle is a newly discovered autotrophic CO2 fixation pathway based on the reversal of TCA cycle, in which citrate synthase catalyzes the thermodynamically unfavorable citrate cleavage reaction. In this work, we proposed that radicals promote C-C bond cleavage of citrate in roTCA cycle based on series intermediate catalytic state of citrate synthases from Desulfurella acetivoran (DaCS) and Thermosulfidibacter takaii (TtCS) obtained by electron paramagnetic resonance (EPR) and X-ray crystallography. We also proposed that the peroxo-bridge like interaction promotes C-C bond generation between acetyl group and oxaloacetate in citrate synthesis reaction based on intermediate state of human citrate synthase by time-resolved characteristic Raman spectroscopy and X-ray diffraction methods. Results also indicate these mechanisms would be widespread among conserved citrate synthases.