Fig. 1.

A schematic illustration of the receptor-mediated endocytosis and viral budding processes. In modeling clathrin-independent, receptor-mediated endocytosis, Gao et al. (8) assume that once binding between a particle and the plasma membrane is initiated, the particle with immobilized ligands attracts and binds to progressively more receptors on the cell surface. Depletion of free receptors in the vicinity of the contact zone drives diffusion of receptors toward the zone, where they bind particle ligands, bringing more of the membrane into contact with the particle until the entire particle is engulfed by the plasma membrane. With some modifications, this model may be applicable to other biological problems, such as viral budding, in which the viral capsid is wrapped outward into a vesicle by means of membrane-bound envelope proteins.