title: The Most Prevalent Freeman-Sheldon Syndrome Mutations in the Embryonic Myosin Motor Share Functional Defects.
abstract: The embryonic myosin isoform is expressed during fetal development and rapidly down-regulated after birth. Freeman-Sheldon syndrome (FSS) is a disease associated with missense mutations in the motor domain of this myosin. It is the most severe form of distal arthrogryposis, leading to overcontraction of the hands, feet, and orofacial muscles and other joints of the body. Availability of human embryonic muscle tissue has been a limiting factor in investigating the properties of this isoform and its mutations. Using a recombinant expression system, we have studied homogeneous samples of human motors for the WT and three of the most common FSS mutants: R672H, R672C, and T178I. Our data suggest that the WT embryonic myosin motor is similar in contractile speed to the slow type I/β cardiac based on the rate constant for ADP release and ADP affinity for actin-myosin. All three FSS mutations show dramatic changes in kinetic properties, most notably the slowing of the apparent ATP hydrolysis step (reduced 5-9-fold), leading to a longer lived detached state and a slowed Vmax of the ATPase (2-35-fold), indicating a slower cycling time. These mutations therefore seriously disrupt myosin function.
authors.affiliation: From the School of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom and.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Walklate
authors.affiliation: the Department of Molecular and Developmental Biology, University of Colorado, Boulder, Colorado 80309.
authors.forename: Carlos
authors.initials: C
authors.lastname: Vera
authors.affiliation: From the School of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom and.
authors.forename: Marieke J
authors.initials: MJ
authors.lastname: Bloemink
authors.affiliation: From the School of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom and M.A.Geeves@kent.ac.uk.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Geeves
authors.affiliation: the Department of Molecular and Developmental Biology, University of Colorado, Boulder, Colorado 80309 leslie.leinwand@Colorado.edu.
authors.forename: Leslie
authors.initials: L
authors.lastname: Leinwand
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002478:Cells, Cultured; D003394:Craniofacial Dysostosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D003598:Cytoskeletal Proteins / Q000235:genetics* / Q000378:metabolism; D000066473:Embryonic Germ Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D009119:Muscle Contraction / Q000502:physiology*; D009154:Mutation / Q000235:genetics*; D015879:Myosin Subfragments / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms
chemical_list: D003598:Cytoskeletal Proteins; C510594:MYH3 polypeptide, human; D015879:Myosin Subfragments; D020033:Protein Isoforms; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases
keywords: ATPase; enzyme kinetics; human myosin; molecular motor; muscle disease; myosin subfragment 1; recombinant protein expression; skeletal muscle; transient kinetics