A Directed TM→JM Coupling in Receptor Tyrosine Kinase Dimers, Set by Activating Mutations and the Membrane Environment

Abstract The direction of conformational coupling in a membrane protein, that is, which domain drives which, has been inaccessible to experimental measurement. We recover this directivity from molecular dynamics (MD) of transmembrane–juxtamembrane (TM–JM) dimers of receptor tyrosine kinases EGFR and FGFR3. Coupling is detected with a Bayesian network framework (CASCADE); its direction is measured with PERI (Phase-plane Estimation of Rotational Irreversibility) as the net phase-plane circulation, validated on synthetic data, and resolved at 0.1 ns. Direction is summarized as the TM→JM directed-mass fraction f+ (0.5 = balanced) via a hierarchical Bayesian model. The activating TM mutants EGFR L658Q and FGFR3 A391E are TM→JM (posterior probabilities: 0.95 and 0.99); fluid wild-type EGFR leans the same way (0.93), in agreement with its experimentally reported constitutive activity in fluid but not ordered bilayers; the ligand-dependent ordered wild-type is balanced (0.45); and an activating mutation raises the TM→JM bias above the ordered wild-type with probability 0.94. The directivity thus tracks the measured activity state of the receptor, distinguishing signaling-competent from ligand-dependent RTK dimers by a property not apparent from structure alone.