Functional effects of the hypertrophic cardiomyopathy R403Q mutation are different in an alpha- or beta-myosin heavy chain backbone

J Biol Chem. 2008 Jul 18;283(29):20579-89. doi: 10.1074/jbc.M800554200. Epub 2008 May 13.


The R403Q mutation in the beta-myosin heavy chain (MHC) was the first mutation to be linked to familial hypertrophic cardiomyopathy (FHC), a primary disease of heart muscle. The initial studies with R403Q myosin, isolated from biopsies of patients, showed a large decrease in myosin motor function, leading to the hypothesis that hypertrophy was a compensatory response. The introduction of the mouse model for FHC (the mouse expresses predominantly alpha-MHC as opposed to the beta-isoform in larger mammals) created a new paradigm for FHC based on finding enhanced motor function for R403Q alpha-MHC. To help resolve these conflicting mechanisms, we used a transgenic mouse model in which the endogenous alpha-MHC was largely replaced with transgenically encoded beta-MHC. A His(6) tag was cloned at the N terminus of the alpha-and beta-MHC to facilitate protein isolation by Ni(2+)-chelating chromatography. Characterization of the R403Q alpha-MHC by the in vitro motility assay showed a 30-40% increase in actin filament velocity compared with wild type, consistent with published studies. In contrast, the R403Q mutation in a beta-MHC backbone showed no enhancement in velocity. Cleavage of the His-tagged myosin by chymotrypsin made it possible to isolate homogeneous myosin subfragment 1 (S1), uncontaminated by endogenous myosin. We find that the actin-activated MgATPase activity for R403Q alpha-S1 is approximately 30% higher than for wild type, whereas the enzymatic activity for R403Q beta-S1 is reduced by approximately 10%. Thus, the functional consequences of the mutation are fundamentally changed depending upon the context of the cardiac MHC isoform.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Arginine / genetics
  • Arginine / metabolism
  • Ca(2+) Mg(2+)-ATPase / metabolism
  • Cardiomyopathy, Hypertrophic / genetics
  • Cardiomyopathy, Hypertrophic / metabolism*
  • Gene Expression Regulation / drug effects
  • Mice
  • Mice, Transgenic
  • Models, Molecular
  • Mutation / genetics
  • Myosin Heavy Chains / genetics
  • Myosin Heavy Chains / isolation & purification
  • Myosin Heavy Chains / metabolism*
  • Propylthiouracil / pharmacology
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Protein Structure, Quaternary
  • Ventricular Myosins / genetics
  • Ventricular Myosins / isolation & purification
  • Ventricular Myosins / metabolism*


  • Protein Isoforms
  • Propylthiouracil
  • Arginine
  • Ca(2+) Mg(2+)-ATPase
  • Ventricular Myosins
  • Myosin Heavy Chains