Mutation-Dependent Conformational Dynamics and Dual-Mode Afatinib Binding in EGFR Exon 19 Variants

Exon 19 mutations in the epidermal growth factor receptor (EGFR) kinase domain, including the common ΔE746-A750 deletion and the less frequent L747P substitution, are clinically important drivers of non-small cell lung cancer (NSCLC). Although these mutations occur within the β3-αC region, how they alter EGFR conformational dynamics and influence the response to the covalent inhibitor afatinib remains incompletely understood. Here, we investigated mutation-dependent changes in EGFR conformational ensembles, dual-mode of afatinib binding, and Cys797-mediated covalent reaction energetics in wild-type, ΔE746-A750, and L747P kinase domains. We find that both mutations preferentially stabilize active-like kinase conformations but do so through distinct structural mechanisms. The ΔE746-A750 deletion produces greater P-loop and ATP-pocket conformational heterogeneity, whereas L747P restricts αC-helix and activation-loop dynamics and more strongly stabilizes the active-like ensemble. Afatinib binding disrupts the K745-E762 interaction and alters the αC-helix conformation while the pre-formed covalent state samples αC-out configurations that increase accessibility of an αC-adjacent pocket that is less accessible in the apo state. Alchemical calculations further reveal mutation- and protonation-state-dependent differences in the conditional noncovalent binding free energy of afatinib. QM/MM calculations of Cys797-afatinib bond formation reveal mutation-dependent differences in the calculated reaction barrier, with L747P showing a lower barrier than ΔE746-A750 within the employed QM/MM model. Together, these results show that EGFR exon 19 mutations reshape the conformational landscape and local structural environment of the kinase, thereby influencing afatinib binding and the energetic environment of covalent bond formation. These findings provide a structural framework for understanding how distinct EGFR mutations can produce different responses to covalent kinase inhibition.