title: Molecular mechanical differences between isoforms of contractile actin in the presence of isoforms of smooth muscle tropomyosin.
abstract: The proteins involved in smooth muscle's molecular contractile mechanism - the anti-parallel motion of actin and myosin filaments driven by myosin heads interacting with actin - are found as different isoforms. While their expression levels are altered in disease states, their relevance to the mechanical interaction of myosin with actin is not sufficiently understood. Here, we analyzed in vitro actin filament propulsion by smooth muscle myosin for [Formula: see text]-actin ([Formula: see text]A), [Formula: see text]-actin-tropomyosin-[Formula: see text] ([Formula: see text]A-Tm[Formula: see text]), [Formula: see text]-actin-tropomyosin-[Formula: see text] ([Formula: see text]A-Tm[Formula: see text]), [Formula: see text]-actin ([Formula: see text]A), [Formula: see text]-actin-tropomyosin-[Formula: see text] ([Formula: see text]A-Tm[Formula: see text]), and [Formula: see text]-actin-tropomoysin-[Formula: see text] ([Formula: see text]A-Tm[Formula: see text]). Actin sliding analysis with our specifically developed video analysis software followed by statistical assessment (Bootstrapped Principal Component Analysis) indicated that the in vitro motility of [Formula: see text]A, [Formula: see text]A, and [Formula: see text]A-Tm[Formula: see text] is not distinguishable. Compared to these three 'baseline conditions', statistically significant differences ([Formula: see text]) were: [Formula: see text]A-Tm[Formula: see text] - actin sliding velocity increased 1.12-fold, [Formula: see text]A-Tm[Formula: see text] - motile fraction decreased to 0.96-fold, stop time elevated 1.6-fold, [Formula: see text]A-Tm[Formula: see text] - run time elevated 1.7-fold. We constructed a mathematical model, simulated actin sliding data, and adjusted the kinetic parameters so as to mimic the experimentally observed differences: [Formula: see text]A-Tm[Formula: see text] - myosin binding to actin, the main, and the secondary myosin power stroke are accelerated, [Formula: see text]A-Tm[Formula: see text] - mechanical coupling between myosins is stronger, [Formula: see text]A-Tm[Formula: see text] - the secondary power stroke is decelerated and mechanical coupling between myosins is weaker. In summary, our results explain the different regulatory effects that specific combinations of actin and smooth muscle tropomyosin have on smooth muscle actin-myosin interaction kinetics.
authors.affiliation: Dept. Physiology, McGill University, Montréal, Québec, Canada ; Centre for Applied Mathematics in Bioscience and Medicine, Montréal, Québec, Canada ; Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada.
authors.forename: Lennart
authors.initials: L
authors.lastname: Hilbert
authors.forename: Genevieve
authors.initials: G
authors.lastname: Bates
authors.forename: Horia N
authors.initials: HN
authors.lastname: Roman
authors.forename: Jenna L
authors.initials: JL
authors.lastname: Blumenthal
authors.forename: Nedjma B
authors.initials: NB
authors.lastname: Zitouni
authors.forename: Apolinary
authors.initials: A
authors.lastname: Sobieszek
authors.forename: Michael C
authors.initials: MC
authors.lastname: Mackey
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Lauzon
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D007700:Kinetics; D008958:Models, Molecular; D009130:Muscle, Smooth; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D013552:Swine; D014335:Tropomyosin / Q000737:chemistry* / Q000378:metabolism*; D014422:Turkeys
chemical_list: D000199:Actins; D020033:Protein Isoforms; D014335:Tropomyosin