Do cardiac actin mutations lead to altered actomyosin interactions?
It is currently hypothesized that increased heart muscle contractility leads to hypertrophic cardiomyopathy (HCM), and reduced contractility leads to dilated cardiomyopathy (DCM). To determine if changes in the core interaction between actin and myosin occur due to mutations in the
cardiac actin gene (ACTC), we measured the interactions between myosin and 8 ACTC mutant proteins found in patients with HCM or DCM. R312H showed a decreased actin-activated myosin S1 ATPase rate (13.1 ± 0.63 μmol/L/min) compared to WT (15.3 ± 1.6 μmol/L/min), whereas the
rate with E99K was significantly higher (20.1 ± 1.5 μmol/L/min). In vitro motility assays with varying ATP concentrations showed that the K
M for E99K remains unchanged with a significantly decreased V
max (1.90 ± 0.37 μm/sec) compared
to WT (3.33 ± 0.46 μm/sec). Based on a 5 nm myosin step size, we calculated a duty ratio of approximately 0.04 for WT and the majority of mutant actins; however, the duty ratio for E99K was twice as high. Based on our analysis of 8 ACTC mutants, we infer that mutations in ACTC lead
to disease through various molecular mechanisms. While changes in actomyosin interactions with the E99K mutation might cause increased ATP usage and tension leading to HCM, measurable changes in the basic interaction between actin and myosin do not appear to be involved in the mechanisms of
disease development for the other ACTC mutants tested.
Keywords: actine cardiaque; actine-myosine; actomyosin; cardiac actin; cardiomyopathie hypertrophique; duty ratio; facteur de marche; hypertrophic cardiomyopathy; mutations
Document Type: Research Article
Publication date: 01 January 2015
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