This laboratory is concerned with the mechanisms, regulation and structure of enzymes, with emphasis on the ways in which structure and mechanism are interrelated. Current research effort is centered on proteins that function as molecular motors, such as the kinesin ATPase, which drives fast axonal transport in nerve cells. In this process, newly synthesized membranes and proteins in the body of the nerve cell are packaged into small membrane vesicles and transported to the synapse by ATP -dependent sliding along tracks of parallel microtubules that run longitudinally down the axon. We are also studying other members of the kinesin superfamily that are likely involved in movements on spindle microtubules during cell division. In addition, many potential ATPase motors have recently been discovered that likely produce movements of nucleic acids and other substrates, and investigation of their mechanism of action and regulation is a direction for future work.

One goal is to determine if there are structural and mechanistic features that are common among different biological motors. Our initial work with kinesin established that the rate limiting step was release of the product ADP rather than hydrolysis of ATP. Furthermore, interaction of the kinesin-ADP complex with microtubules stimulated ADP release in a manner analogous to the stimulation by actin filaments of product release with myosin. In spite of this similarity in overall mechanism, the two motors produce very different types of motility. Kinesin is highly processive (binds to the microtubule and slides long distances along the microtubule without dissociation), while myosin is non-processive (separates from the actin filament during each ATPase cycle). In the course of our investigations of the kinetics of dimer constructs of kinesin, we have discovered that the processive action of kinesin results from a cooperative interaction between the two head (motor) domains such that they alternate in a hand-over-hand manner as they move along the microtubule. Thus the dimer is able to maintain net attachment to the microtubule while the individual head domains can come on and off during each ATPase cycle.

Hackney DD, Stock MF, Moore J, Patterson RA. Modulation of kinesin half-site release and kinetic processivity by a spacer between the head groups. Biochemistry 2003; 42:12011-12018.

Hackney DD. Motor proteins of the kinesin superfamily. The Enzymes, 3th ed. 2003; 23:88-143.

Hackney DD, Stock MF. Kinesin's IAK tail domain inhibits initial microtubule-stimulated ADP release. Nature Cell Biology 2000; 2:257-260.

Hackney DD. Highly processive microtubule-stimulated ATP hydrolysis by dimeric kinesin head domains. Nature 1995; 377:448-450.

Hackney DD. Evidence for alternating head catalysis by kinesin during microtubule- stimulated ATP hydrolysis. Proc. Natl. Acad. Sci. USA 1994; 91:6865-6869.