Mechanistic insights into the interaction of the MOG1 protein with the cardiac sodium channel Na1.5 clarify the molecular basis of Brugada syndrome.

Na1.5 is the α-subunit of the cardiac sodium channel complex. Abnormal expression of Na1.5 on the cell surface because of mutations that disrupt Na1.5 trafficking causes Brugada syndrome (BrS), sick sinus syndrome (SSS), cardiac conduction disease, dilated cardiomyopathy, and sudden infant death syndrome. We and others previously reported that Ran-binding protein MOG1 (MOG1), a small protein that interacts with Na1.5, promotes Na1.5 intracellular trafficking to plasma membranes and that a substitution in MOG1, E83D, causes BrS. However, the molecular basis for the MOG1/Nav1.5 interaction and how the E83D substitution causes BrS remains unknown. Here, we assessed the effects of defined MOG1 deletions and alanine-scanning substitutions on MOG1's interaction with Na1.5. Large deletion analysis mapped the MOG1 domain required for the interaction with Na1.5 to the region spanning amino acids 146-174, and a refined deletion analysis further narrowed this domain to amino acids 146-155. Site-directed mutagenesis further revealed that Asp-148, Arg-150, and Ser-151 cluster in a peptide loop essential for binding to Na1.5. GST pulldown and electrophysiological analyses disclosed that the substitutions E83D, D148Q, R150Q, and S151Q disrupt MOG1's interaction with Na1.5 and significantly reduce its trafficking to the cell surface. Examination of MOG1's 3D structure revealed that Glu-83 and the loop containing Asp-148, Arg-150, and Ser-151 are spatially proximal, suggesting that these residues form a critical binding site for Na1.5. In conclusion, our findings identify the structural elements in MOG1 that are crucial for its interaction with Na1.5 and improve our understanding of how the E83D substitution causes BrS.