title: X-ray recordings reveal how a human disease-linked skeletal muscle α-actin mutation leads to contractile dysfunction.
abstract: In humans, mutant skeletal muscle α-actin proteins are associated with contractile dysfunction, skeletal muscle weakness and a wide range of primarily skeletal muscle diseases. Despite this knowledge, the exact molecular mechanisms triggering the contractile dysfunction remain unknown. Here, we aimed to unravel these. Hence, we used a transgenic mouse model expressing a well-described D286G mutant skeletal muscle α-actin protein and recapitulating the human condition of contractile deregulation and severe skeletal muscle weakness. We then recorded and analyzed the small-angle X-ray diffraction patterns of isolated membrane-permeabilized myofibers. Results showed that upon addition of Ca(2+), the intensity changes of the second (1/19 nm(-1)) and sixth (1/5.9 nm(-1)) actin layer lines and of the first myosin meridional reflection (1/14.3 nm(-1)) were disrupted when the thin-thick filament overlap was optimal (sarcomere length of 2.5-2.6 μm). However these reflections were normal when the thin and thick filaments were not interacting (sarcomere length>3.6 μm). These findings demonstrate, for the first time, that the replacement of just one amino acid in the skeletal muscle α-actin protein partly prevents actin conformational changes during activation, disrupting the strong binding of myosin molecules. This leads to a limited myosin-related tropomyosin movement over the thin filaments, further affecting the amount of cross-bridges, explaining the contractile dysfunction.
authors.affiliation: Centre of Human and Aerospace Physiological Sciences, School of Biomedical Sciences, King's College London, London, United Kingdom. Electronic address: julien.ochala@kcl.ac.uk.
authors.forename: Julien
authors.initials: J
authors.lastname: Ochala
authors.affiliation: Harry Perkins Institute of Medical Research, The University of Western Australia, Nedlands, Australia.
authors.forename: Gianina
authors.initials: G
authors.lastname: Ravenscroft
authors.affiliation: Harry Perkins Institute of Medical Research, The University of Western Australia, Nedlands, Australia.
authors.forename: Elyshia
authors.initials: E
authors.lastname: McNamara
authors.affiliation: Harry Perkins Institute of Medical Research, The University of Western Australia, Nedlands, Australia.
authors.forename: Kristen J
authors.initials: KJ
authors.lastname: Nowak
authors.affiliation: Japan Synchrotron Radiation Research Institute, SPring8, Hyogo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Iwamoto
mesh_terms: D000199:Actins / Q000235:genetics*; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000235:genetics*; D018908:Muscle Weakness / Q000235:genetics*; D018482:Muscle, Skeletal / Q000473:pathology*; D009154:Mutation; D009210:Myofibrils / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D014335:Tropomyosin / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D000199:Actins; D014335:Tropomyosin; D009218:Myosins
keywords: Actin; Muscle disease; Myosin; Small-angle X-ray scattering