Cryo-EM captures the coordination of long-range allostery and asymmetric electron transfer by a bi-copper cluster in the nitrogenase-like DPOR complex

Abstract

Enzymes that catalyze long-range electron transfer reactions are often structurally evolved to possess two symmetrical halves. The functional advantages and mechanistic principles for such architecture remain a mystery. Using Cryo-EM we capture snapshots of the nitrogenase-like Dark-operative Protochlorophyllide Oxidoreductase (DPOR) enzyme during substrate recognition and turnover. The structures reveal that asymmetry is enforced upon substrate binding and leads to an allosteric inhibition of protein-protein interactions and electron transfer in one half. Residues that form a conduit for electron transfer are aligned in one half while misaligned in the other. An ATP-turnover coupled switch is triggered once electron transfer is accomplished in one half and relayed through a bi-copper cluster at the oligomeric interface, leading to activation of enzymatic events in the other. The findings provide a mechanistic blueprint for regulation of asymmetric long-range electron transfer. One-Sentence SummaryA bi-copper cluster coordinates electron transfer for substrate reduction in the nitrogenase-like DPOR enzyme and the structures reveal how allostery and asymmetry are enacted over 100[A] and utilized for sequential electron transfer.