Progesterone receptor membrane component 1 (PGRMC1) regulates Heme trafficking through mitochondria-ER junctions

Heme is a cofactor essential for a multitude of biological reactions. The terminal step of heme synthesis occurs in the mitochondrial matrix which means that heme must be trafficked from there to other locales in the cell. Thus, identifying intracellular heme chaperones is crucial to understanding regulation of global cellular metabolism. The heme-binding protein progesterone receptor membrane component 1 (PGRMC1) has been proposed to function as a chaperone for several biologically active molecules including heme, but its cellular role is not fully understood. Here, we investigate the function of PGRMC1 in heme metabolism. By monitoring intracellular heme location and concentrations in Saccharomyces cerevisiae, we show that mutants lacking damage associated protein 1 (Dap1), the yeast ortholog of PGRMC1, have altered nuclear heme trafficking which can be corrected by complementation with DAP1 or PGRMC1. Biochemical analyses reveal that PGRMC1 co-localizes with known mitochondrial-associated membrane (MAM) proteins and proteomic comparison of interaction partners shows enrichment of MAM-associated proteins and pathways. Metabolomics profiling of wild-type and PGRMC1 knockout cells identifies significant changes of several metabolites, including heme, several amino acids, long chain acyl-carnitine, ethanolamine phosphate, and mevalonic acid. Together, these results provide evidence that PGRMC1 is involved in heme trafficking and homeostasis through MAMs.