Vladimir Lupashin and Elizabeth Sztul
The movement of proteins between compartments of the secretory and endocytic \r\npathways occurs via vesicles and/or larger carriers. The efficacy of both pathways relies on high fidelity with which the vesicles are delivered to the appropriate target membrane. The initial recognition between a vesicle and a target membrane appears to be mediated by members of loosely related family of tethering factors. Tethering factors can be generally divided into a group of long coiled-coil proteins and a group of large multi-subunit complexes. In both cases, the tethers can span relatively long distances (>200 nm) between the vesicle and the acceptor membrane. As such, they may provide a molecular net to catch relevant vesicles and increase the possibility that they will fuse with the appropriate membrane. In addition, tethers may have additional roles in facilitating the formation of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes, promoting cargo selection, and regulating the interactions of membrane carriers with the cytoskeleton. This review will focus on functions of tethering factors in vesicle-mediated transport. We describe the current understanding of tethering at distinct sites of the secretory and endocytic pathways.