(347g) Impact of Defect Creation and Motion On the Large-Scale Reorganization Dynamics of Self-Assembled Clathrin Lattices

Clathrin is a protein that plays a major role in the creation of membrane-bound transport vesicles in cells. Clathrin forms soccer-ball-shaped lattices that coat a new vesicle as it forms. The clathrin molecule is known to take the shape of a triskelion, a pinwheel-shaped structure with three bent legs. In vitro assembly of clathrin within a solution results in closed, nanoscale assemblies with various shapes and sizes. We develop a theoretical model for the thermodynamics and kinetics of clathrin self-assembly.  Our model addresses the behavior in two dimensions and can be easily extended to three dimensions, facilitating the study of membrane, surface, and bulk assembly.  The clathrin triskelia are modeled as flexible pinwheels that form leg-leg associations and resist bending and stretching deformations.  Thus, the pinwheels are capable of forming a range of ring structures, including 5-, 6-, and 7-member rings that are observed experimentally.  Our theoretical model employs Brownian dynamics to track the motion of clathrin pinwheels at sufficiently long time scales to achieve complete assembly.  Invoking theories of dislocation-mediated melting in two dimensions, we discuss the phase behavior for clathrin self-assembly as predicted by our theoretical model.  We demonstrate that the generation of $5$-$7$ defects in an otherwise perfect honeycomb lattice resemble creation of two dislocations with equal and opposite Burgers vectors, and we use orientational- and translational-order correlation functions to predict the crystalline-hexatic and hexatic-liquid phase transitions in clathrin lattices.  These results illustrate the pivotal role that molecular elasticity plays in the physical behavior of self-assembling and self-healing materials.