Sarah Rice
Title: Assistant Professor
Research area: Functions of Molecular Motor Tails
Degree: Ph.D.
Voice: 312.503.5390
Fax: 312.503.7912
e-mail: s-rice@northwestern.edu

Detailed research description:
The long-term goals of my laboratory’s research are to understand the functions of molecular motor tails in detail, and to understand how the function of a motor’s tail, combined with the function of its head, enables it to fulfill its role in the cell.

While the detailed stepping mechanisms of several molecular motors are well known, the mechanisms by which they perform their duties in the cell are more complex and much less well-characterized. The reason for this is that the tail domains of motors, which have functions such as assembly of motors into larger structures, cargo binding, and regulation, are poorly understood. My laboratory’s research seeks to begin elucidating the function of molecular motor tail domains by focusing in on two fairly well-characterized motors, myosin II and conventional kinesin. We will ask the following questions: How does the myosin-II tail assemble into bipolar thick filaments? At what stage of assembly does myosin-II become functional in the cell? How does the kinesin tail reversibly block motility by the head? When and where does this self-regulation by kinesin take place in the cell?

My laboratory will begin studying the myosin tail to determine the structure of myosin bipolar thick filaments in molecular detail. The mechanism underlying the self-assembly of myosin-II bipolar thick filaments is not fully understood and their final structure after assembly is not known. This gap in our knowledge of myosin-II structure results in a gap in our understanding of the pathology of myosin-related diseases such as familial hypertrophic cardiomyopathy. We will use mutagenesis, electron microscopy, and chemical crosslinking to examine the structure of myosin-II bipolar thick filaments, and we will also design a molecule with the assembly characteristics of a myosin-II BPTF by mutating a coiled-coil scaffold that does not assemble.

Conventional kinesin is a molecular motor that translates the energy of ATP hydrolysis into unidirectional transport of its cargo. The tail and light chain domains of conventional kinesin regulate its activity when the motor is not cargo-bound in the cell, but the mechanism by which they perform this regulation is not completely understood. Mutations in kinesin and proteins that interact with it have been implicated in several diseases, including colon cancer, Alzheimer’s disease, and neurofibromatosis. Understanding how kinesins are regulated in the cell may lead to new therapeutics for these diseases. Our long-term goal is to have a detailed structural understanding of how the kinesin tail and light chain domains regulate the motor’s activity.

The current research in my laboratory focuses on the idea that a direct interaction of the kinesin tail with the head is likely to be the cause of the drastic effects on kinesin’s ATPase and microtubule-binding activity that occur when the motor is regulated. We will use mutagenesis and chemical crosslinking to determine exactly which amino acids of the tail and/or light chains interact with the head, and we will perform EPR (electron paramagnetic resonance) and FRET (fluorescence resonance energy transfer) spectroscopy to detect conformational changes that take place upon regulation

Representative publications:

Rice, S., Lin, A.W., Safer, D., Hart, C.L., Naber, N., Carragher, B.O., Cain, S.M., Pechatnikova, E., Wilson-Kubalek, E.M., Whittaker, M., Pate, E., Cooke, R., Taylor, E.W., Milligan, R.A., and Vale, R.D. (1999). A structural change in the kinesin motor protein that drives motility. Nature 402, 778-784.

Case, R.B., Rice, S., Hart, C.L., Ly, B., and Vale, R.D. (2000). Role of the kinesin neck linker and catalytic core in microtubule-based motility. Current Biology 10(3), 157-160.

Rock, R.S., Rice, S., Wells, A.L., Purcell, T.J., Spudich, J.A., Sweeney, H. L. (2001). Myosin VI is a processive motor with a large step size. PNAS 98(24):13655-13659.

Sindelar, C.V., Budny, M.J., Rice, S., Fletterick, R.J., and Cooke, R. (2002). Two conformations in the human kinesin powerstroke defined by X-ray crystallography and EPR spectroscopy. Nature Structural Biology, 9:844-848.

Rice, S., Cui, Y., Sindelar, C., Naber, N., Matuska, M., Vale, R., and Cooke, R. (2003). Thermodynamic properties of the kinesin neck region docking to the catalytic core. Biophysical Journal 84(3), 1844-1854.

Naber, N., Rice, S., Matuska, M., Vale, R.D., Cooke, R., and Pate, E. (2003).EPR spectroscopy shows a microtubule-dependent conformational change in the switch I domain. Biophysical Journal 84(5), 3190-6.

Naber, N., Minehart, T.J., Rice, S., Chen, X., Grammer, J., Matuska M., Vale, R.D., Kollman, P.A., Car, R., Yount, R.G., Cooke, R., Pate, E. (2003). Closing of the nucleotide pocket of kinesin-family motors upon binding to microtubules. Science 300(5620), 798-801.

Rice, S., Purcell, T.J., Spudich, J.A.(2003). Building and using optical traps to study properties of molecular motors. Methods in Enzymology 361A, 112-133.