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COMMENTARY
Shedding light on the dynamics of endocytosis and viral budding

Gang Bao ^, , and X. Robert Bao 

Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332; and Department of Applied Physics, California Institute of Technology, Pasadena, CA 91125

Endocytosis is used by eukaryotic cells to perform a wide range of functions, including the uptake of extracellular nutrients and the regulation of cell-surface receptors, as well as by toxins, viruses, and microorganisms to gain entry into cells (1). Endocytosis actually encompasses many different processes, such as phagocytosis of large (>250 nm) particles as well as pinocytosis of large volumes of fluid (2). One of the most important endocytic mechanisms is a receptor-mediated process whereby the plasma membrane binds specific macromolecules and smaller particles by means of specialized receptors, invaginates around those particles, and then pinches off to form small vesicles. Receptor-mediated endocytosis had been thought to be assisted by specific proteins, either clathrin or caveolin, polymerizing into a spherical shell around the invagination (3). Recently, however, evidence has arisen for a different, clathrin- and caveolin-independent route by which endocytosis may occur (4, 5). The understanding and quantitative analysis of the mechanisms underlying receptor-mediated endocytosis have important implications for not only viral pathogenesis but also the delivery of macromolecules and nanoparticles for intracellular imaging and targeted therapies (6).

View larger version (18K): [in this window] [in a new window]   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, . . . [Full Text of this Article]

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Companion article to this Commentary:

From The Cover: Mechanics of receptor-mediated endocytosis

Huajian Gao, Wendong Shi, and Lambert B. Freund
PNAS 2005 102: 9469-9474. [Abstract] [Full Text]