  We present a coarse-grained model of clathrin that is simple enough to be
computationally tractable yet includes key observed qualitative features: a
triskelion structure with excluded volume between legs; assembly of polymorphic
cages in the bulk; formation of buds on a membrane. We investigate the assembly
of our model using both Monte Carlo simulations and molecular dynamics with
hydrodynamic interactions, in the latter employing a new membrane boundary
condition. In the bulk, a range of known clathrin structures are assembled. A
membrane budding pathway involving the coalescence of multiple small clusters
is identified.
