Structural Studies of Dynamin-Related Protein 1 (DRP1) Provide Mechanistic Insight into Mitochondrial Fission.

Abstract

Dynamin-related protein 1 (Drp1) belongs to a family of large GTPase proteins that regulate membrane dynamics and morphology. Drp1 localizes to mitochondrial constriction sites in vivo to facilitate outer membrane fission, and mutations that inhibit its activity lead to hyper-fused mitochondria in vivo. Direct inhibition of Drp1 protects against cell death by limiting increased mitochondrial fission associated with apoptosis. Using cryo-electron microscopy (cryo-EM), previous studies of the yeast homolog of Drp1, Dnm1, were used to determine its structural properties. Dnm1 was shown to form large (>100 nm in diameter) helical oligomers that constrict upon GTP hydrolysis to generate a contractile force on the underlying membrane. Similar methods are now being used to gain mechanistic insight into the mammalian mitochondrial fission complex. Several similarities and differences have been found between the yeast and mammalian systems. In solution, Drp1 forms stable tetramers, which represent the pre-assembled state of Drp1. The size of this complex (∼330 kDa) provides a suitable target for 3D image reconstruction. Additional interactions with GTP analogs and/or synthetic liposomes promote Drp1 self-assembly into extended helical oligomers. The 3D structures of these helices will be determined to elucidate interactions that mediate Drp1 self-assembly. The effects of GTP hydrolysis on the Drp1 helical oligomers are also being studied to determine how Drp1 promotes outer mitochondrial membrane fission. Future studies will examine interactions between Drp1 and partner proteins in the mitochondrial fission complex.