Understanding the Structural Basis of Epha1 and Epha2 Homo‐Dimerization, Membrane Proximal Domain Interactions and its Implications for Cancer

Abstract

EphA1 and EphA2 are receptor tyrosine kinases which play a critical role in cellular growth, differentiation and cell motility. In line with the mRNA expression in multiple tissues and organs, the overexpression of these receptors has been reported in several different cancer types, and even in cancer‐derived cell lines. This makes them key therapeutic targets for treatment of several cancers. In Eph receptors, ligand binding regulates the monomer‐dimer equilibrium through stabilization of the dimeric state by inducing a conformational change in the extracellular region (ECR). Thus, dimerization is a key regulatory step in the activity and signaling process of these receptors. However, the involvement of the transmembrane (TM), the immediate two extracellular FibronectinIII domains (FN1&2) and the juxtamembrane (JM) region in the dimerization process is not clearly defined [1]. Moreover, it is clear that the FN domains and the JM region also functions in synergy with the TM domain for signal transduction. The JM domain has several basic residues (K/R) that are closely positioned to the membrane surface, while the surface of the EphA2 2nd FN domain has also been reported to interact with the lipid bilayer. Therefore, studying the structural mechanisms of EphA1 and EphA2 dimerization and membrane interactions will help us better understand the activity and signaling of these receptors in different cancer types. Importantly, working with membrane proteins is extremely challenging. However, the recent developments in molecular dynamics simulation have provided a powerful tool to study membrane proteins and their interactions. Here, we modeled the relevant domains of the EphA1 and EphA2 receptors and studied their structural mechanism of activation by using the coarse‐grain (CG) molecular dynamics simulations using the recently published Martini3 potential function [2]. We show that the Fibronectin domains, TM and JM domains all differ in their interactions and in their interactions with the membrane between EphA1 and A2. Furthermore, the FN domains constrain the TM region of EphA2 to be non‐dimeric in many of the simulations, whereas FN domain dimerization and membrane orientation is more compatible with TM helix dimers in EphA1. The underlying differences in the primary sequence which are likely responsible for these observations as well as future directions of the project are discussed.