Capturing the Sequential Steps of Dynamin-mediated Fission by Cryo-EM: The Mixed Blessing of Helical Polymers
Jenny E. Hinshaw, Ph.D.
Senior Investigator, Structural Cell Biology Section,
Laboratory of Cell and Molecular Biology, NIDDK
12:00 PM – Thursday, July 11, 2019
Dynamin superfamily proteins (DSPs) are present in all organisms and are broadly implicated in membrane remodeling, actin dynamics and innate immunity. DSPs are mechanochemical GTPases whose function is dependent on oligomerization of the protein and conformational changes that occur during the GTP hydrolysis cycle. Dynamin, the founding member of this superfamily, is crucial for endocytosis, synaptic membrane recycling, membrane trafficking within the cell, and cytokinesis. The emerging model entails dynamin assembling around the necks of budding vesicles as a helical polymer and upon GTP hydrolysis, undergoes a significant constriction that ultimately leads to membrane fission. In the past, we solved a 3.8 Å resolution cryo-EM structure of a dynamin-lipid helical polymer in the GTP-bound state. Compared to the soluble crystal structure of the tetramer, membrane bound dynamin1 adopts a more extended form, with the GTPase and Pleckstrin Homology domains positioned more distal from the central core of the protein. Our structure defines the dynamin asymmetric-dimer (building block) and how the dimer assembles into a polymer. The structure also reveals a novel asymmetry within the dimer as a result of a severely bent helix in only one monomer. More recently, we solved a 4.6 Å structure of a dynamin mutant in a super-constricted state, illustrating how a shift from a 1-start to 2-start helix leads to further constriction of the membrane. These molecular snapshots of the biologically relevant form of dynamin provide a framework for understanding the complex orchestration of GTP-driven conformational changes that mediate membrane constriction.