David D. Hackney
614 Mellon Institute
Department of Biological Sciences
Carnegie Mellon University
4400 Fifth Avenue
Pittsburgh, PA 15213
Ph.D., University of California, Berkeley
Postdoctoral Appointment, University of California, Los Angeles
Our 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 conventional kinesin-1 ATPase, which moves a range of cargo molecules along tracks of microtubules from the interior of cells to the periphery. Although kinesin-1 plays a role in all types of eukaryotic cells, it is especially important in nerve cells because of their elongated geometry. Most proteins and membranes are synthesized in the cell body of a nerve cell, but must be transported long distances down the axon and dendrites to reach the synapses. Kinesin-1 is a major motor for driving this long distance transport. We are interested both in the mechanism of kinesin as a motor (see below) and in how it is regulated, including how it selects what cargoes to bind and transport. An important aspect of regulation is that kinesin-1 is autoinhibited through the binding of a tail domain to the motor domains to inhibit their ATPase. Although each kinesin-1 has two motor domains and two tail domains, we discovered that only one of the two tail domains binds to the two motor domains to produce an inhibited complex. This biochemical result has been confirmed by the X-ray structure of the complex determined by our collaborators. This structure suggested that inhibition results from constraint on the relative movements of the motor domains produced by the additional cross-linking at the position of the tail binding. A covalent mimic of this constraint was shown to be sufficient for inhibition in the absence of tail domains. This work has opened a wide range of additional studies that are in progress: If only one tail domain binds to the motors, what is the other tail domain doing? How does cargo binding in the tail region influence the autoihibition? Can a ternary complex of motors, tail and cargo be formed? Do dimeric cargoes bind to both tails or only to the tail that is not bound to the motors?
The second major goal is to account for the biophysical properties of kinesin, as a motor, based on its biochemical properties that couple the steps of ATP hydrolysis to the binding and conformational changes that produced movement and force, especially at the single molecule level. This study relies heavily on single turnover experiments by stopped flow and FRET and other spectroscopic probes for binding and conformational changes. The rates in the hydrolysis direction have been determined, but it is much more difficult to determine the 'back' rates for ATP resynthesis because the hydrolysis reaction is so highly favored. An additional important approach is the use of isotopic exchange methods to determine these 'back' rates of ATP resynthesis that are needed to determine the free energy changes at each step.
Work is also directed at other members of the kinesin superfamily such as Eg5/BimC that is required for proper alignment of microtubules in the spindle during cell division and helicases that produce rearrangements of nucleic acid structures. In addition, many other potential ATPase motors have been discovered and investigation of their mechanism of action and regulation are being explored as new areas of focus.
Kaan HY, Hackney DD, Kozielski F. The Structure of the Kinesin-1 Motor-Tail Complex Reveals the Mechanism of Autoinhibition. Science. 333, 883-885, 2011.
Cao W, Coman MM, Ding S, Henn A, Middleton ER, Bradley MJ, Rhoades E, Hackney DD, Pyle AM, De La Cruz EM. Mechanism of Mss116 ATPase Reveals Functional Diversity of DEAD-Box Proteins. J. Mol. Biol. 409, 399-414, 2011.
Hackney DD, Baek N, and Snyder AC. Half-site inhibition of dimeric kinesin head domains by monomeric tail domains, Biochemistry. 48, 3448-3456, 2009.
Kaan HY, Ulaganathan V, Hackney DD, Kozielski F. An Allosteric Transition Trapped in an Intermediate State of a New Kinesin-Inhibitor Complex. Biochem. J. 425, 55-60, 2009.
Hackney DD and Stock MF. Kinesin tail domains and Mg2+ directly inhibit release of ADP from head domains in the absence of microtubules, Biochemistry. 47, 7770-7778, 2008.
Hackney DD. Processive motor movement, Science. 316, 58-59, 2007.
Olivares AO, Chang W, Mooseker MS, Hackney DD and De La Cruz EM. The tail domain of myosin Va modulates actin binding to one head, J.Biol.Chem. 281, 31326-31336, 2006.
Skoufias DA, De Bonis S, Lebeau L, Crevel I, Cross R, Wade RH, Hackney DD, Kozielski F. S-Trityl-L-Cysteine Is a Reversible, Tight-Binding Inhibitor of the Human Kinesin Eg5 That Specifically Blocks Mitotic Progression. J. Biol. Chem. 2006.
Hackney DD. The tethered motor domain of a kinesin-microtubule complex catalyzes reversible synthesis of bound ATP, Proc.Natl.Acad.Sci.U.S.A 102, 18338-18343, 2005.
Browning H, Hackney DD. The EB1 Homolog Mal3 Stimulates the ATPase of the Kinesin Tea2 by Recruiting It to the Microtubule. J. Biol. Chem. 280, 12299-12304, 2005.
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. 42, 12011-12018, 2003.
Hackney DD. Motor proteins of the kinesin superfamily. The Enzymes, 3th ed., 23:88-143, 2003.
Hackney DD, Stock MF. Kinesin's IAK Tail Domain Inhibits Initial Microtubule-Stimulated ADP Release. Nat. Cell Biol. 2, 257-260, 2000.
Hackney DD. Highly processive microtubule-stimulated ATP hydrolysis by dimeric kinesin head domains. Nature, 377:448-450, 1995.