BARRIER-FREE PATHS OF DIRECTED PROTEIN MOTION IN THE ERYTHROCYTE PLASMA-MEMBRANE

A model is presented for the steric interaction between a plasma membr ane protein and the membrane cytoskeleton in the human erythrocyte. Th e cytoskeleton is treated as a network of polymer chains attached to a Rat bilayer, and the membrane protein is a hemisphere of effective ra dius R(e) with center on the bilayer edge. The simulation is used to i nvestigate the barrier-free path L for linear guided motion of a prote in in the bilayer plane. It is shown that the barrier-free paths of sm all proteins can be used to extract the effective in-plane diameter of cytoskeletal components. For example, the in-plane diameter of an ank yrin attachment site is found to be approximately 12 nm in the simulat ion, or twice the computational spectrin diameter. The barrier-free pa ths of large proteins (R(e) > 23 nm) vanish when the proteins are corr alled by the cytoskeleton. For intermediate size proteins, L decreases approximately as L proportional to S--1.4 where S is proportional to the sum of the protein and cytoskeleton chain radii.