Molecular mechanism for the interaction of MOG1 with the intracellular loop II of cardiac sodium channel Nav1.5 and its role in arrhythmias.

SCN5A encodes the cardiac sodium channel α-subunit Na_v1.5, and its variants cause long QT syndrome (LQTS), Brugada syndrome (BrS) and other arrhythmias. MOG1 interacts with Na_v1.5 to increase cardiac sodium current densities, however, molecular mechanisms remain poorly defined. The objectives of this study were to identify the crucial structural elements responsible for the interaction between MOG1 and Na_v1.5 intracellular Loop II, and determine the significance of this interaction to cardiac arrhythmias. Whole-cell patch-clamping was used to record sodium current I_Na in tsA201 and neonatal rat primary cardiomyocytes. Glutathione S-transferase (GST) pull-down assays were used to characterize protein-protein interactions. Mutagenesis was used to create deletions and point mutations. Characterization of large deletions and small deletions of Na_v1.5 Loop II 940-1200 defined the MOG1-interacting domain to V1190-H1200. Point mutation analysis revealed that amino acids R₁₁₉₅, Y₁₁₉₉ and H₁₂₀₀ were involved in MOG1-Na_v1.5 Loop II interaction. Two variants of MOG1-interacting domain from human patients showed important functional effects. Variant p.R1195C was identified in two individuals with cardiac arrhythmias in ClinVar, weakened the interaction between Na_v1.5 and MOG1, and reduced MOG1-enhanced cardiac sodium current densities. Variant p.Y1199S was identified in one individual with LQTS and one with cardiac arrhythmias, generated late I_Na, weakened the interaction between Na_v1.5 and MOG1, and reduced MOG1-enhanced cardiac sodium current densities. This study identifies three critical amino acids R₁₁₉₅, Y₁₁₉₉ and H₁₂₀₀ of Na_v1.5 Loop II for interaction with MOG1, and reveals the molecular mechanisms by which variants p.R1195C and p.Y1199S in MOG1-interacting domain cause LQTS and cardiac arrythmias.