Molecular motors and their tracks
Dr. Kathy Trybus received her Ph.D. in 1981 from the University of Chicago in Biophysics. She next went to Brandeis University and worked in a Structural Biology lab in the Rosenstiel Basic Medical Sciences Research Center. In 1998, Dr. Trybus joined the Department faculty at University of Vermont.
A major focus of the laboratory is unconventional myosin V, a processive motor that moves cargo along actin for long distances without dissociating. Two class V myosins from budding yeast (called Myo2p and Myo4p) have captured our interest, since both had been characterized to be non-processive, despite being demonstrated cargo transporters.
Using single molecule and biochemical techniques, we recently showed that Myo2p can only move processively when it walks on actin tracks that resemble those found in the cell. In this case, yeast tropomyosin was found to be essential for the motor to move processively -- an elegant demonstration of how the track can affect the motor.
Myo4p, a single-headed class V myosin in budding yeast, transports mRNA to the bud tip. We showed that an oligomeric adapter protein that links the motor to the cargo (She2p) recruits two motors to form a processive complex. Addition of mRNA cargo greatly stabilizes the complex, so that only motors with cargo can move processively. We are altering the mRNA cargo to understand why localizing mRNAs have multiple "zipcode" elements.
Vertebrate myosin Va undergoes a folded (inactive) to extended (active) conformational transition. We are investigating if cargo binding is sufficient to activate the motor, using myoVa-melanophilin-Rab27a-melanosome as a model system.
Another major focus is to understand the molecular mechanisms by which point mutations in smooth muscle actin (ACTA2) lead to vascular disease. These studies are made possible by our ability to express homogeneous wild-type and mutant vertebrate actins in the baculovirus/insect cell expression system. Techniques used to assess defects caused by the mutations include: a TIRF based assay that follows polymerization of single actin filaments in real time, measurement of persistence length to assess structural changes in the filament, and motility assays to quantify how fast smooth muscle myosin can move the actin filaments .
Tropomyosin is essential for Myo2p, a class V myosin in budding yeast, to move processively on actin.
Interactions between two molecular motors coupled to a DNA scaffold.
Nelson SR, Trybus KM, Warshaw DM (2014) Motor coupling through lipid membranes enhances transport velocities for ensembles of myosin Va. Proc Natl Acad Sci U S A in press.
Sladewski T, Trybus K (2014) A single molecule approach to mRNA transport by a class V myosin. RNA Biol 11(8): .
Efremov AK, Radhakrishnan A, Tsao DS, Bookwalter CS, Trybus KM, Diehl MR (2014) Delineating cooperative responses of processive motors in living cells. Proc Natl Acad Sci U S A 111(3): E334-43.
Taylor KA, Feig M, Brooks CL 3rd, Fagnant PM, Lowey S, Trybus KM (2014) Role of the essential light chain in the activation of smooth muscle myosin by regulatory light chain phosphorylation. J Struct Biol 185(3): 375-82.
Clayton JE, Pollard LW, Sckolnick M, Bookwalter CS, Hodges AR, Trybus KM, Lord M (2014) Fission yeast tropomyosin specifies directed transport of myosin-V along actin cables. Mol Biol Cell 25(1): 66-75.
DeBerg HA, Blehm BH, Sheung J, Thompson AR, Bookwalter CS, Torabi SF, Schroer TA, Berger CL, Lu Y, Trybus KM, Selvin PR (2013) Motor domain phosphorylation modulates kinesin-1 transport. J Biol Chem 288(45): 32612-21.
Sckolnick M, Krementsova EB, Warshaw DM, Trybus KM (2013) More than just a cargo adapter, melanophilin prolongs and slows processive runs of myosin Va. J Biol Chem 288(41): 29313-22.
Department of Molecular Physiology & Biophysics
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