Disease-associated mutations and alternative splicing alter the enzymatic and motile activity of nonmuscle myosins II-B and II-C

J Biol Chem. 2005 Jun 17;280(24):22769-75. doi: 10.1074/jbc.M503488200. Epub 2005 Apr 20.


Human families with single amino acid mutations in nonmuscle myosin heavy chain (NMHC) II-A (MYH9) and II-C (MYH14) have been described as have mice generated with a point mutation in NMHC II-B (MYH10). These mutations (R702C and N93K in human NMHC II-A, R709C in murine NMHC II-B, and R726S in human NMHC II-C) result in phenotypes affecting kidneys, platelets, and leukocytes (II-A), heart and brain (II-B), and the inner ear (II-C). To better understand the mechanisms underlying these defects, we characterized the in vitro activity of mutated and wild-type baculovirus-expressed heavy meromyosin (HMM) II-B and II-C. We also expressed two alternatively spliced isoforms of NMHC II-C which differ by inclusion/exclusion of eight amino acids in loop 1, with and without mutations. Comparison of the actin-activated MgATPase activity and in vitro motility shows that mutation of residues Asn-97 and Arg-709 in HMM II-B and the homologous residue Arg-722 (Arg-730 in the alternatively spliced isoform) in HMM II-C decreases both parameters but affects in vitro motility more severely. Analysis of the transient kinetics of the HMM II-B R709C mutant shows an extremely tight affinity of HMM for ADP and a very slow release of ADP from acto-HMM. Although mutations generally decreased HMM activity, the R730S mutation in HMM II-C, unlike the R730C mutation, had no effect on actin-activated MgATPase activity but decreased the rate of in vitro motility by 75% compared with wild type. Insertion of eight amino acids into the HMM II-C heavy chain increases both actin-activated MgATPase activity and in vitro motility.

MeSH terms

  • Actins / chemistry
  • Adenosine Diphosphate / chemistry
  • Alternative Splicing*
  • Animals
  • Arginine / chemistry
  • Asparagine / chemistry
  • Ca(2+) Mg(2+)-ATPase / chemistry
  • Dose-Response Relationship, Drug
  • Genetic Vectors
  • Humans
  • Insecta
  • Kinetics
  • Mice
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Mutation*
  • Myosin Heavy Chains / chemistry
  • Myosin Heavy Chains / genetics*
  • Myosin Subfragments / chemistry
  • Myosin Type II / chemistry
  • Myosin Type II / genetics*
  • Myosins / chemistry
  • Nonmuscle Myosin Type IIB / chemistry*
  • Nonmuscle Myosin Type IIB / genetics*
  • Phenotype
  • Point Mutation
  • Protein Isoforms
  • Protein Structure, Tertiary
  • Recombinant Proteins / chemistry


  • Actins
  • MYH14 protein, human
  • Myh14 protein, mouse
  • Myosin Subfragments
  • Protein Isoforms
  • Recombinant Proteins
  • Adenosine Diphosphate
  • Asparagine
  • Arginine
  • Ca(2+) Mg(2+)-ATPase
  • Myosin Type II
  • Nonmuscle Myosin Type IIB
  • Myosin Heavy Chains
  • Myosins