Complex sentence: PGRMC1 shares key structural motifs with cytochrome b 5, a heme binding protein that activates P450 proteins, which are important in drug, hormone and lipid metabolism.
Split into simpler sentences: PGRMC1 shares key structural motifs with cytochrome b 5. PGRMC1 binds and activates P450 proteins, which are important in drug, hormone and lipid metabolism.