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SIAM Chapter Seminar

Zachary McDargh
Carnegie Mellon University
Title: What can geometry tell us about dynamin-mediated fission?

Abstract: Any cellular fission process is completed when the neck connecting almost-separate membrane compartments is severed. This crucial step is somehow accomplished by proteins from the dynamin family, which polymerize into helical spirals around such necks. Much research has been devoted to elucidating the specifics of that somehow, but despite no shortage of ideas, the question is not settled. Pictorially obvious notions of strangling or pushing are difficult to render in mechanically precise terms. Moreover, since dynamin is able to convert use GTP for fuel, it is tempting to speculate that it has a motor activity that assists the necessary severing action; however the underlying mechanics is not obvious. We believe the difficulty to be the mechanically nontrivial nature of confining elastic filaments onto curved surfaces, for which efficient methods to conceptualize the associated forces and torques have only recently appeared. Here we investigate the implications of a conceptually simple yet mechanically challenging model: consider an elastic helical filament confined to a surface mimicking the neck between two membrane compartments, which we assume to take the shape of a catenoid. We use numerical and perturbative solutions to the filaments shape equation to calculate the expected length of such adsorbed filaments, their shapes, and the forces they exert, as a function of the key parameters in the model. While real dynamin is surely more complex, we consider such a minimal model to be the indispensable baseline. Without knowing what such a model can and cannot explain, it is difficult to justify more complex mechanisms, or understand the constraints under which this machinery evolved in the first place.

Date: Thursday, March 17, 2016
Time: 5:30 pm
Location: Wean Hall 8220
Submitted by:  Samuel Cohn