Dissection of porphyrin-induced conformational dynamics in the heme biosynthesis enzyme ferrochelatase.

Human ferrochelatase (EC 4.99.1.1) catalyzes the insertion ferrous iron into protoporphyrin IX as the last step in heme biosynthesis, an essential process to most organisms given the vast intracellular functions of heme. Even with multiple ferrochelatase structures available, the exact mechanism for iron insertion into porphyrin is still a matter for debate. It is clear, however, that conformational dynamics are important for porphyrin substrate binding, initial chelation of iron, insertion of iron into the macrocycle, and release of protoheme IX. In this work we characterize conformational and dynamic changes in ferrochelatase associated with porphyrin binding using the substrate mesoporphyrin (MPIX) and backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS). In general, regions surrounding the active site become more ordered from direct or indirect interactions with the porphyrin. Our results indicate that the lower lip of the active site mouth is preorganized for efficient porphyrin bind...