Dataset Information

The propensity for tropomyosin twisting in the presence and absence of F-actin.

ABSTRACT: A canonical model of muscle ?-tropomyosin (Tpm1.1), based on molecular-mechanics and electron microscopy of different contractile states, shows that the two-stranded coiled-coiled is pre-bent to present a specific molecular-face to the F-actin filament. This conformation is thought to facilitate both filament assembly and tropomyosin sliding across actin to modulate myosin-binding. However, to bind effectively to actin filaments, the 42 nm-long tropomyosin coiled-coil is not strictly canonical. Here, the mid-region of tropomyosin twists an additional ?20° in order to better match the F-actin helix. In addition, the N- and C-terminal regions of tropomyosin polymerize head-to-tail to form continuous super-helical cables. In this case, 9 to 10 residue-long overlapping domains between adjacent molecules untwist relative to each other to accommodate orthogonal interactions between chains in the junctional four-helix nexus. Extensive molecular dynamics simulations show that the twisting and untwisting motions of tropomyosin vary appreciably along tropomyosin length, and in particular that substantial terminal domain winding and unwinding occurs whether tropomyosin is bound to F-actin or not. The local and regional twisting and untwisting do not appear to proceed in a concerted fashion, resembling more of a "wringing-type" behavior rather than a rotation.

SUBMITTER: Rynkiewicz MJ

PROVIDER: S-EPMC5064861 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

The propensity for tropomyosin twisting in the presence and absence of F-actin.

Rynkiewicz Michael J MJ Fischer Stefan S Lehman William W

Archives of biochemistry and biophysics 20160920

A canonical model of muscle α-tropomyosin (Tpm1.1), based on molecular-mechanics and electron microscopy of different contractile states, shows that the two-stranded coiled-coiled is pre-bent to present a specific molecular-face to the F-actin filament. This conformation is thought to facilitate both filament assembly and tropomyosin sliding across actin to modulate myosin-binding. However, to bind effectively to actin filaments, the 42 nm-long tropomyosin coiled-coil is not strictly canonical. ...[more]

PMID: 27663225

Similar Datasets

Project description: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.

Project description:Filamentous actin (F-actin) is the major protein of muscle thin filaments, and actin microfilaments are the main component of the eukaryotic cytoskeleton. Mutations in different actin isoforms lead to early-onset autosomal dominant non-syndromic hearing loss, familial thoracic aortic aneurysms and dissections, and multiple variations of myopathies. In striated muscle fibres, the binding of myosin motors to actin filaments is mainly regulated by tropomyosin and troponin. Tropomyosin also binds to F-actin in smooth muscle and in non-muscle cells and stabilizes and regulates the filaments there in the absence of troponin. Although crystal structures for monomeric actin (G-actin) are available, a high-resolution structure of F-actin is still missing, hampering our understanding of how disease-causing mutations affect the function of thin muscle filaments and microfilaments. Here we report the three-dimensional structure of F-actin at a resolution of 3.7 Å in complex with tropomyosin at a resolution of 6.5 Å, determined by electron cryomicroscopy. The structure reveals that the D-loop is ordered and acts as a central region for hydrophobic and electrostatic interactions that stabilize the F-actin filament. We clearly identify map density corresponding to ADP and Mg(2+) and explain the possible effect of prominent disease-causing mutants. A comparison of F-actin with G-actin reveals the conformational changes during filament formation and identifies the D-loop as their key mediator. We also confirm that negatively charged tropomyosin interacts with a positively charged groove on F-actin. Comparison of the position of tropomyosin in F-actin-tropomyosin with its position in our previously determined F-actin-tropomyosin-myosin structure reveals a myosin-induced transition of tropomyosin. Our results allow us to understand the role of individual mutations in the genesis of actin- and tropomyosin-related diseases and will serve as a strong foundation for the targeted development of drugs.

Dataset Information

The propensity for tropomyosin twisting in the presence and absence of F-actin.

Publications

The propensity for tropomyosin twisting in the presence and absence of F-actin.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets