Substrate and Product Pathways in Monomeric and Dimeric Aromatase

Lisandra L. Martin 1; Rageshwari R. Marolika 1,2,3; Paul D. O’Leary 1; Ajay S. Panwar 3
1 School of Chemistry, Monash University, Clayton, Victoria, 3800, Australia
2 IITB-Monash Research Academy, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
3 Department of Metallurgical Engineering and Material Sciences, Indian Institute of Technology Bombay Powai, Mumbai 40076, India

Aromatase (P450arom, CYP19A1) is a cytochrome P450 enzyme that plays a crucial role in the rate-limiting step of oestrogen biosynthesis from androgens. Aromatase is one of only a few multi-functional cytochrome P450 enzymes and is capable of a three-step oxidative process, that achieves aromatisation of the steroid A-ring. Despite the importance of this enzyme, there remains a paucity of data on how multi-functional activity is accomplished, at least at the molecular level. Some data suggests that aromatase can homodimerise thus aiding the multi-step reaction mechanism.1,2
This study explores the structural and functional dynamics of monomeric and dimeric human aromatase in a lipid bilayer, focusing on substrate (androstenedione) entry and product (oestrone) exit pathways. Using Accelerated Molecular Dynamics, Steered Molecular Dynamics, and umbrella sampling simulations, distinct energetic preferences were identified. The dimeric form stabilises substrate entry via inter-subunit interactions, favouring a pathway associated with a dimeric form of aromatase, while the monomeric form allows efficient product exit through another pathway. Whilst dimerisation of human aromatase enhances substrate entry and stabilises product transition, while the monomeric form remains functional but less efficient. These findings raise the possibility that oscillations between monomeric and dimeric forms are involved in aromatase achieving a three-step oxidation process. The results also have potential implications for drug design by targeting specific pathways or stabilizing enzyme forms. Factors that influence aromatase activity cane be better understood and essential to understand reproduction across many species.

1. Praporski, S., Ng, S., Nguyen, A., Corbin, C.J., Mechler, A., Zheng, J., Conley, A.J., Martin, L.L., Organization of Enzymes Involved in Sex Steroid Synthesis: Protein-protein interactions in lipid layers, J. Biol. Chem. (2009), 284(48) 33224-33232.
2. Martin LL, Holien JK, Mizrachi D, Corbin CJ, Conley AJ, Parker MW, Rodgers RJ, Evolutionary comparisons predict that dimerization of cytochrome P450 aromatase increases enzymatic activity and efficiency, J Steroid Biochem. Mol. Biol. (2015) 154, 294-301.