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Biophys J, September 2001, p. 1360-1372, Vol. 81, No. 3
*Humboldt-Universität zu Berlin,
Mathematisch-Naturwissenschaftliche Fakultät I, Institut
für Biologie/Biophysik, D-10115 Berlin, and
Humboldt-Universität zu Berlin, Charite, Bereich
Medizin, Institut für Biochemie, D-10117 Berlin, Germany
Studies on fusion between cell pairs have provided
evidence that opening and subsequent dilation of a fusion pore are
stochastic events. Therefore, adequate modeling of fusion pore
formation requires a stochastic approach. Here we present stochastic
simulations of hemagglutinin (HA)-mediated fusion pore formation
between HA-expressing cells and erythrocytes based on numerical
solutions of a master equation. The following elementary processes are
taken into account: 1) lateral diffusion of HA-trimers and receptors,
2) aggregation of HA-trimers to immobilized clusters, 3) reversible
formation of HA-receptor contacts, and 4) irreversible conversion of
HA-receptor contacts into stable links between HA and the target
membrane. The contact sites between fusing cells are modeled as
superimposed square lattices. The model simulates well the statistical
distribution of time delays measured for the various intermediates of
fusion pore formation between cell-cell fusion complexes. In
particular, these are the formation of small ion-permissive and
subsequent lipid-permissive fusion pores detected experimentally (R. Blumenthal, D. P. Sarkar, S. Durell, D. E. Howard, and
S. J. Morris, 1996, J. Cell Biol. 135:63-71).
Moreover, by averaging the simulated individual stochastic time courses
across a larger population of cell-cell-complexes the model also
provides a reasonable description of kinetic measurements on lipid
mixing in cell suspensions (T. Danieli, S. L. Pelletier, Y. I. Henis, and J. M. White, 1996, J. Cell Biol.
133:559-569).
Biophys J, September 2001, p. 1360-1372, Vol. 81, No. 3
© 2001 by the Biophysical Society 0006-3495/01/09/1360/13 $2.00
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