Membrane traffic: Microtubule motor cycles and kinectin

Abstract

Although membrane traffic can occur in the absence of microtubules, the rapid metabolism of many eucaryotic cells requires that vesicular organelles are actively transported. Microtubule-dependent transport is particularly robust in actively growing cells and the volume of membrane transported increases dramatically in going from static to growth conditions. Both inward and outward movement are regulated simultaneously implying coordinate activation of both motors or a transport cycle. Relatively large complexes of the microtubule motors and associated proteins are responsible for powering the movements (reviewed in Vallee and Sheetz, 1996). Of the many motors that have been described, kinesin and cytoplasmic dynein are the most abundant and have been the focus of these studies. Included in the microtubule motor complexes are motor receptors and activating factors. A membranous motor receptor, kinectin, was identified on the basis of its interaction with kinesin (Toyoshima et al., 1992). An antibody to kinectin blocks both kinesin binding to organelles and kinesin-dependent motility of those organelles (Kumar et al., 1995).