A mutation associated with Charcot-Marie-Tooth disease enhances the formation of stable dynamin 2 complexes in cells
Mutations in dynamin 2 (DNM2) have been associated with two distinct motor disorders, Charcot-Marie-Tooth neuropathies (CMT) and centronuclear myopathy (CNM). The majority of these mutations are clustered in the pleckstrin homology domain (PHD) which engage in intramolecular interactions that suppress dynamin self-assembly and GTPase activation. CNM mutations in the PHD interferes with these intramolecular interactions, thereby blocking the formation of the auto-inhibited state. CMT mutations are located primarily on the opposite surface of the PHD, which is specialized for lipid PIP2 binding. It has been speculated that the distinct locations and interactions of residues mutated in CMT and CNM explain why each set of mutations cause either one disease or the other, despite their close proximity within the PHD sequence. We show that at least one CMT-causing mutant, lacking residues 555DEE557 ({Delta}DEE), displays this inability to undergo auto-inhibition as observed in CNM-linked mutants. This {Delta}DEE deletion mutant induces the formation of abnormally large cytoplasmic inclusions similar to those observed for CNM-linked mutant R369W. We also found substantially reduced migration from the membrane of the {Delta}DEE deletion mutant. These findings call into question the molecular mechanism currently believed to underlie the absence of pathogenic overlap between DNM2-dependent CMT and CNM.