Structure function and regulation of the microtubule motors dynein and kinesin

Dynein is a 1.2 MDa microtubule based motor protein that uses the energy released by the hydrolysis of adenosine triphosphate to move cargoes towards the minus-ends of MTs. Dynein is composed of multiple polypeptides including dynein heavy chains, dynein intermediate chains as well as other polypeptides that play a role in the selection of cargos. The dynein heavy chain is responsible for the hydrolysis of adenosine triphosphate as well as movement along microtubules. The dynein intermediate chain plays a role in the dimerization of the dynein molecule as well as in binding to cargoes such as the dynein activator dynactin. Dynactin is another megadalton complex that interacts with dynein and functions as an adaptor protein allowing dynein to move more processively and carry a larger array of cargoes. Like dynein, dynactin consists of multiple polypeptides. The p150 subunit of dynactin is a mostly coiled-coil protein that has been identified as the polypeptide responsible for increasing the processivity of dynein in vitro. Opposing the minus-end directed motion of the dynein/dynactin complex is the plus-end directed motor kinesin. Kinesin is considerably smaller in size than dynein but moves in a more processive manner than dynein. Since dynein and kinesin move in opposing fashions along microtubules a mechanism of regulation must exist that permits each motor to move in the appropriate location and at the appropriate time.;The study presented here focuses on the regulation of microtubule-based motors on three different levels. Using the model organism Neurospora crassa the role of specific amino acids within the microtubule binding domain of dynein will be analyzed to determine their role in the regulation of microtubule-attachment and microtubule-release. The next section will focus on the role accessory factors, such as dynactin and Bicaudal D2, play in regulating the motility of dynein. The final section will focus on the differential regulation of dynein and kinesin by the fibrous microtubule associated protein tau. The goal of these studies is to provide a more complete understanding of how molecular motors function and how they are regulated.