Phase Separation of the Variable Domain of Dynamin Related Protein 1 in TMAO Suggests a Role in Assembly

Abstract

The Dynamin superfamily is a class of large GTPases that perform essential membrane remodeling events via self-assembly stimulated GTP hydrolysis in a manner that involves the coordination of lipid-membrane interaction, high-order oligomerization, and GTP hydrolysis, however a clear understanding of how these functions are coordinated has remained elusive. A “variable domain” (VD) is present in many superfamily members and may enable specific targeting to sites of action, but the nature of VD function is unclear in most dynamins. Dynamin-related protein 1 (Drp1) is the primary mechanoenzyme responsible for mitochondrial fission. We seek to identify the role of the Drp1 VD, or VD. We find that removal of the VD from Drp1 results in enhanced assembly and GTP hydrolysis, suggesting that the VD has an auto-inhibitory role. We find that the VD is intrinsically disordered (ID) and surprisingly, undergoes phase separation or coacervation under conditions that induce other ID proteins to fold. The same conditions that induce phase separation of the VD also enhance binding to cardiolipin, a lipid that is unique to the mitochondrial membrane. Based on these findings we suggest a model in which the VD inhibit Drp1 assembly by dynamically occluding assembly interfaces, and that this auto-inhibition is relieved upon interaction of the VD with cardiolipin at the mitochondrial membrane, involving the process of coacervation. This model may also be applicable to other members of the dynamin superfamily, and intrinsically disordered membrane remodeling proteins in general.