Visualization of cargo concentration by COPII minimal machinery in a planar lipid membrane.
ABSTRACT Selective protein export from the endoplasmic reticulum is mediated by COPII vesicles. Here, we investigated the dynamics of fluorescently labelled cargo and non-cargo proteins during COPII vesicle formation using single-molecule microscopy combined with an artificial planar lipid bilayer. Single-molecule analysis showed that the Sar1p-Sec23/24p-cargo complex, but not the Sar1p-Sec23/24p complex, undergoes partial dimerization before Sec13/31p recruitment. On addition of a complete COPII mixture, cargo molecules start to assemble into fluorescent spots and clusters followed by vesicle release from the planar membrane. We show that continuous GTPase cycles of Sar1p facilitate cargo concentration into COPII vesicle buds, and at the same time, non-cargo proteins are excluded from cargo clusters. We propose that the minimal set of COPII components is required not only to concentrate cargo molecules, but also to mediate exclusion of non-cargo proteins from the COPII vesicles.
Article: Hierarchical global optimization of quasiseparable systems: application to Lennard-Jones clusters.[show abstract] [hide abstract]
ABSTRACT: An unbiased hierarchical global optimization (GO) method for quasiseparable systems is presented. In such systems the coordinates of a set of nearby local minima approximately describe the coordinates of a much larger set of surrounding local minima. This allows one to reduce the original GO problem to a much simpler GO subproblem that uses the coordinates of the local minima to reduce the search space and simplify its landscape. The algorithm showed excellent performance in tests on "difficult cases" of Lennard-Jones (LJ) clusters. Putative global minima of LJ500 and LJ1000 are obtained.Physical Review E 09/2002; 66(2 Pt 2):025701. · 2.26 Impact Factor