A Molecular Motor for Microtubule-Dependent Organelle Transport in Neurospora crassa
Kinesin and cytoplasmic dynein are two types of microtubule-dependent molecular motors that are involved in a variety of transport phenomena within eukaryotic cells. The former generally moves towards the plus end of microtubules, while the movement of the latter is minus-end-directed. Both classes of motor molecules comprise superfamilies or families of related proteins that have diversified considerably during evolution. The kinesin superfamily is defined by its founding member, the motor protein kinesin first identified in the squid Loligo (Vale et al. 1985). Kinesin has a globular motor domain that possesses the ATP and microtubule binding sites, an α- helical stalk, and a tail domain. Two of these “heavy chains” associate with one an-other via their stalk domains to form a molecule whose overall shape resembles that of a myosin molecule (Schliwa 1989). The tail domains are further associated with one copy each of a “light chain”, the function of which has not been elucidated with certainty. All members of the kinesin superfamily share the putative motor head domain (usually 35–45% identity). However, the stalk/tail domains may be vastly different from each other. The general belief is that this variability within the tail domains reflects different functions or binding affinities of the respective motors. In many cases, this belief is indeed supported by experimental evidence.
KeywordsMigration Sucrose Filtration Sedimentation Vanadate
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