Vesicular Coat Proteins
The secretory pathway is a transport system that shuttles
macromolecules between the different compartments in a cell. Movement
between intracellular compartments is carried out by transport
vesicles that bud from one compartment and fuse with another in a highly
organized manner allowing net movement of cargo in a unidirectional,
prescribed pattern.
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Many
of the components required for vesicular transport have been identified
by biochemical methods in higher eukaryotic cells, or by genetic analysis
in the yeast Saccharomyces cerevisiae. Three types of coated vesicles
are known, each with a different type of protein coat and each formed
by reversible polymerization of a distinct set of protein subunits under
carefully regulated conditions. Each type of vesicle transports proteins
from particular parent organelles to particular destination organelles.
Clathrin-coated vesicles form from the plasma membrane and the trans-Golgi
network and move to late endosomes. They also mediate the transport from
the trans-Golgi network to the lysosome. COPII-coated vesicles transport
proteins from the rough endoplasmatic reticulum to the Golgi, whereas
COPI-coated vesicles mainly transport proteins in the retrograde direction
between Golgi cisternae and from the cis-Golgi back to the rough ER. The
coat proteins surrounding transport vesicles that move from the late endosome
to lysosomes and to the plasma membrane have not yet been identified.
We are using single particle electron microscopy to elucidate how individual
coat proteins associate with each other to form vesicular coats. The highly
ordered clathrin cages are particularly amenable to this approach.
 COPII |
 Clathrin |