Poster Presentation 21st International Conference on Biological Inorganic Chemistry 2025

Heme binding and protein dimerization in progesterone receptor membrane component 1: establishing the relevance of the membrane (#564)

Katlyn K Meier 1 , Prajakta Badve 1 , Opeyemi O Isaac 1
  1. University of Miami, Coral Gables, FLORIDA, United States

The progesterone receptor membrane component 1 (PGRMC1) protein is highly expressed in heme rich organs and is implicated in a variety of functions including drug metabolism, iron homeostasis, and membrane trafficking.1-9 PGRMC1 binds heme and is thought to interact with downstream cytochrome P450s to disrupt drug metabolism and cholesterol synthesis.3 However, prior work has called into question the requirement of heme-binding to trigger formation of the PGRMC1 dimer that is thought to be critical for these interactions.4 We set out to achieve the following objectives: (i) establish spectroscopic benchmarks for heme binding in the cytoplasmic domain, (ii) define and quantify the contribution of heme binding 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 address these outstanding questions, 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, led us to conclude that there are multiple pathways involving disulfide bonding and heme-heme stacking that contribute to PGRMC1 dimerization.10 More recently, we are leveraging tailored nanodisc architectures along with FL-PGRMC1 to address the question of whether the membrane-bound protein can form dimers through the two dominant routes identified previously. Thus far we have established that the full-length protein is able to dimerize, even in the absence of heme, and that these dimers are stable and resistant to reduction by common thiol-containing reducing agents. Results of these studies shed light on the PGRMC1 monomer and dimer and provide a solid foundation to understand how they may participate in downstream protein−protein interactions. In the long-term, these studies will provide critical insight needed to develop design principles for potential therapeutics that target PGRMC1 dimerization and inhibit protein-protein interactions.

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