ABSTRACT Heme is an essential cofactor required for a plethora of cellular processes in eukaryotes. In metazoans the heme biosynthetic pathway is typically partitioned between the cytosol and mitochondria, with the first and final steps taking place in the mitochondrion. The pathway has been extensively studied, and all the biosynthetic enzymes have been structurally characterized to varying extents. Nevertheless, our understanding of the regulation of heme synthesis and factors that influence this process in metazoans remains incomplete. Herein we investigate the molecular organization as well as the catalytic and structural features of the terminal pathway enzyme, ferrochelatase (Hem15), in the yeast Saccharomyces cerevisiae . Biochemical and genetic analyses reveal dynamic association of Hem15 with Mic60, a core component of the mitochondrial contact site and cristae organizing system (MICOS). Loss of MICOS negatively impacts Hem15 activity and results in accumulation of highly reactive and potentially toxic tetrapyrrole precursors that may result in oxidative damage. Restoring intermembrane connectivity in MICOS-deficient cells mitigates these cytotoxic effects. Our data provide new insights into how heme biosynthetic machinery is organized and regulated, linking mitochondrial architecture-organizing factors to heme homeostasis.

Mitochondrial Contact Site and Cristae Organizing System (MICOS) Machinery Supports Heme Biosynthesis by Enabling Optimal Performance of Ferrochelatase