  We investigate the effect of mobile polymer brushes on proteins embedded in
biological membranes by employing both Asakura-Oosawa type of theoretical model
and coarse-grained molecular dynamics simulations. The brush polymer-induced
depletion attraction between proteins changes non-monotonically with the size
of brush. The depletion interaction, which is determined by the ratio of
protein size to the grafting distance between brush polymers, increases
linearly with brush size as long as the polymer brush height is shorter than
the protein size. When the brush height exceeds the protein size, however, the
depletion attraction among proteins is slightly reduced. We also explore the
possibility of brush polymer-induced assembly of a large protein cluster, which
can be related to one of many molecular mechanisms underlying recent
experimental observations of integrin nanocluster formation and signaling.
