Kathleen M. Trybus, Ph.D.
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.
Pollard LW, Bookwalter CS, Tang Q, Krementsova EB, Trybus KM, Lowey S (2017) Fission yeast myosin Myo2 is down-regulated in actin affinity by light chain phosphorylation. Proc Natl Acad Sci U S A 114(35): E7236-E7244.
Liu Z, Chang AN, Grinnell F, Trybus KM, Milewicz DM, Stull JT, Kamm KE (2017) Vascular disease-causing mutation, smooth muscle α-actin R258C, dominantly suppresses functions of α-actin in human patient fibroblasts. Proc Natl Acad Sci U S A 114(28): E5569-E5578.
Lombardo AT, Nelson SR, Ali MY, Kennedy GG, Trybus KM, Walcott S, Warshaw DM (2017) Myosin Va molecular motors manoeuvre liposome cargo through suspended actin filament intersections in vitro. Nat Commun 8: 15692.
Krementsova EB, Furuta K, Oiwa K, Trybus KM, Ali MY (2017) Small teams of myosin Vc motors coordinate their stepping for efficient cargo transport on actin bundles. J Biol Chem 292(26): 10998-11008.
Milewicz DM, Trybus KM, Guo DC, Sweeney HL, Regalado E, Kamm K, Stull JT (2017) Altered Smooth Muscle Cell Force Generation as a Driver of Thoracic Aortic Aneurysms and Dissections. Arterioscler Thromb Vasc Biol 37(1): 26-34.
Ali MY, Vilfan A, Trybus KM, Warshaw DM (2016) Cargo Transport by Two Coupled Myosin Va Motors on Actin Filaments and Bundles. Biophys J 111(10): 2228-2240.
Lu H, Fagnant PM, Krementsova EB, Trybus KM (2016) Severe Molecular Defects Exhibited by the R179H Mutation in Human Vascular Smooth Muscle α-Actin. J Biol Chem 291(41): 21729-21739.