Title: Heme Binding and Protein Dimerization in Progesterone Receptor Membrane Component 1: Establishing the Relevance of the Membrane

Abstract: Progesterone receptor membrane component 1 (PGRMC1) protein is highly expressed in heme-rich organs and is implicated in a diverse biological processes including drug metabolism, iron homeostasis, and membrane trafficking. PGRMC1 binds heme and is thought to interact with downstream cytochrome P450 enzymes to modulate drug metabolism and cholesterol synthesis. However, the requirement of heme-binding to trigger PGRMC1 dimerization and facilitate these interactions remains a topic of debate. This study aimed to: (i) establish spectroscopic bench-marks for heme binding in the cytoplasmic domain, (ii) determine the contribution of heme bind-ing to PGRMC1 dimer formation, (iii) identify alternative pathways en route to the dimer, and (iv) evaluate the impact of biological membranes on dimerization of the full-length protein (FL-PGRMC1). To achieve these objectives, we used a combination of spectroscopic techniques to provide insight into the secondary, quaternary, and metal-centric levels. These data, along with studies of several variants, revealed multiple dimerization mechanisms involving both disulfide bonding and heme-heme stacking. Building on these data, we used tailored nanodisc architec-tures to investigate whether FL-PGRMC1 dimerizes via these routes and whether the membrane influences oligomerization. Thus far, our results show that the full-length protein forms stable di-mers, even in the absence of heme, and that these dimers are resistant to reduction by common thiol-containing reducing agents. Results of these studies clarify the factors that influence PGRMC1 dimerization, provide a solid foundation to understand how PGRMC1 dimers may par-ticipate in downstream protein−protein interactions, and promise to provide the critical insight needed to develop design principles for potential therapeutics that target PGRMC1 dimerization and inhibit protein-protein interactions.

See more of Dr. Meier's research on her website: https://chemistry.as.miami.edu/research-groups/meier-research-group/index.html