  Exocytosis is a common transport mechanism via which cells transport out
non-essential macro-molecules (cargo) into the extra cellular space. ESCRT-III
proteins are known to help in this. They polymerize into a conical spring like
structure and help deform the cell membrane locally into a bud which wrapps the
outgoing cargo. we model this process using a continuum energy functional. It
consists of elastic energies of the membrane and the semi-rigid ESCRT-III
filament, favorable adhesion energy between the cargo and the membrane, and
affinity among the ESCRT-III filaments. We take the free energy minimization
route to identify the sequence of composite structures which form during the
process. We show that membrane adhesion of the cargo is the driving force for
this budding process and not the buckling of ESCRT-III filaments from flat
spiral to conical spring shape. However ESCRT-III stabilizes the bud once it
forms. Further we conclude that a non-equilibrium process is needed to pinch
off/separate the stable bud (containing the cargo) from the cell body.
