Aug 26, 12:00 PM: James Sellers, PhD, NHLBI, NIH, Probing the motile & mechanical ...
Three nonmuscle myosin-2 (NM2) paralogs participate in many mammalian cellular phenomena. Here we compare the mechanical properties of NM2A and NM2B. Each form 310nm bipolar filaments containing 30 myosins. The two paralogs can also co-assemble into the same filament. Both are slow enzymatically compared to most other myosins, but NM2A moves actin filaments 2 to 3 times faster than NM2B in motility assays and NM2B has a higher duty ratio. Neither NM2A nor NM2B demonstrate processive movements as single molecules. We assayed the ability of filaments of these two myosins to move processively on actin filaments bound to a cov! erslip surface. NM2B filaments move processively and experiments show that when co-polymerized with headless tail fragments about 6 motors per half filament are required for processive movements. NM2A filaments require the presence of methylcellulose to increase viscosity in order to move processively. When assayed at low loads by optical trapping NM2A and NM2B give single attachment events with lifetimes of about 1 and 3 sec, respectively. Both paralogs show load dependence of their attachment lifetimes. When actin-attached NM2A is subject to loads of 4-6 pN the lifetimes increase to ~10-20 sec. Strikingly, when NM2B molecules are subject to similar loads the attachment lifetimes are 80-300 sec. This differential load dependence may explain the role of NM2B molecules in stress fibers.Date: August 26, 2019Time: 12:00 PM - 1:00 PM