Advances in the Structural and Biochemical Determination of Several Dynamin-Like GTPases

Abstract

Dynamins are a class of GTPase enzymes responsible for the fusion, fission, and vesiculation of lipid membranes throughout the cell. The dynamin-like protein Optic Atrophy 1 (Opa1) is responsible for the fusion of the mitochondrial inner membrane and plays a role in maintaining cristae shape. Atlastin mediates fusion of homotypic three-way junctions in the endoplasmic reticulum (ER). Mutations in these, and other dynamin-like proteins, can lead to neuropathies including Dominant Optic Atrophy, Hereditary Spastic Paraplegia, and Charcot-Marie-Tooth, among others. Currently, structural and biochemical data is limiting for Opa1. In addition, crystal structures of ATL with nucleotide do not entirely explain the GTPase cycle. We have developed a protocol for expressing and purifying biologically relevant and biochemically active shortened isoforms of Opa1 (Opa1GG) in sufficient quantity to begin crystallography and biochemical assays. Furthermore, we have optimized sample prep and begun reconstructions of aproteolytically processed short form, Opa1S, by cryo-EM on a lipid surface and are examining the role nucleotide plays in structural rearrangements. In addition, to verify work performed by x-ray crystallography, we have begun probing the GTPase cycle of Atlastin using single particle cryo-EM methods.