Volume 4 issue 2 February 2003
A Kinetic proof-reading mechanism for Protein sorting
M Weiss and T. Nilsson

Movie 1: Spatio-temporal evolution of sorting and vesicle formation with the kinetic proof-reading, i.e. hydrolysis is allowed. Starting at t = 0 s from uniform distributions of: (a) proteins in the nonsorting state, (b) proteins in the sorting state, and (c) a randomly distributed set of membrane-associated COPI (nonpolymerizable, no cargo bound) the evolution is monitored. As time elapses, empty COPI molecules (black circles) bind cargo in the nonsorting or sorting state (red and green circles, respectively) and are dynamically exchanged with the cytosolic pool of COPI. At t = 100 s a bud of polymerizable COPI has emerged with about three-fold higher local density of correct cargo as compared to the average density on the membrane (arrows). In contrast, the more abundant cargo in the nonsorting state is not enriched in the bud.

Video 1

Movie 2: Same as in movie 1, but with hydrolysis switched off. At t = 100 s a bud of polymerizable COPI has emerged (arrow). The local densities of correct and wrong cargo, however, are similar to the average densities on the membrane (panels a and b), i.e. there is no sorting. This shows that kinetic proof-reading, and thus sorting, has been spoiled upon blocking hydrolysis, while formation of a bud is still comparable to the case when hydrolysis is allowed.

Video 2