Ephrin receptors are receptor tyrosine kinases (RTKs) that regulate cell growth, differentiation, and motility. EphA2, often overexpressed in cancers, is notable for its ligand-independent activation that promotes pro-oncogenic signaling, in contrast to its ligand-dependent mode that restricts cell migration. EphA1, while structurally related, differs in signaling outcomes, raising questions about how structural variations between the two receptors contribute to their distinct functions. Ligand binding drives receptor clustering through conformational changes in the extracellular region (ECR), while tyrosine kinase activation correlates with transmembrane (TM) dimerization. EphA1 and EphA2 differ markedly in their TM domain, juxtamembrane (JM) region, and fibronectin type III repeats (FN1, FN2). To probe the role of these domains in receptor assembly, we performed coarse-grained molecular dynamics (CG-MD) simulations with the Martini 3 force field in membranes containing POPC, POPS, and PIP2. Simulations reveal that basic JM residues remain tightly associated with the membrane, while the EphA2 FN2 domain shows persistent lipid interactions, consistent with experimental data. Interestingly, FN2 alone constrains TM dimerization in both EphA1 and EphA2. Addition of FN1 promotes dimerization, though the extracellular dimer geometries differ between receptors. These differences arise from sequence variation in the FN1-FN2 linker, which alters domain positioning. Our findings underscore the importance of TM-proximal regions in shaping Eph receptor dimerization and signaling. They suggest mechanistic models for the distinct activation modes of EphA1 and EphA2 and provide a framework for experimental testing. This work offers new insight into how extracellular and membrane-proximal interactions regulate Eph receptor signaling, with implications for EphA2-driven oncogenic pathways.
Sahoo et al. (Sun,) studied this question.