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

Abstract

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.

• Authors: Susan Lowey, Leanne M Lesko, Arthur S Rovner, Alex R Hodges, Sheryl L White, Robert B Low, Mercedes Rincon, James Gulick, Jeffrey Robbins
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 283 Issue 29 Pg. 20579-89 (Jul 18 2008) ISSN: 0021-9258 [Print] United States
• PMID: 18480046 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

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

Topics

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