Deletion of 1–43 amino acids in cardiac myosin essential light chain blunts length dependency of Ca²⁺sensitivity and cross-bridge detachment kinetics

Abstract

The role of cardiac myosin essential light chain (ELC) in the sarcomere length (SL) dependency of myofilament contractility is unknown. Therefore, mechanical and dynamic contractile properties were measured at SL 1.9 and 2.2 μm in cardiac muscle fibers from two groups of transgenic (Tg) mice: 1) Tg-wild-type (WT) mice that expressed WT human ventricular ELC and 2) Tg-Δ43 mice that expressed a mutant ELC lacking 1-43 amino acids. In agreement with previous studies, Ca(2+)-activated maximal tension decreased significantly in Tg-Δ43 fibers. pCa(50) (-log(10) [Ca(2+)](free) required for half maximal activation) values at SL of 1.9 μm were 5.64 ± 0.02 and 5.70 ± 0.02 in Tg-WT and Tg-Δ43 fibers, respectively. pCa(50) values at SL of 2.2 μm were 5.70 ± 0.01 and 5.71 ± 0.01 in Tg-WT and Tg-Δ43 fibers, respectively. The SL-mediated increase in the pCa(50) value was statistically significant only in Tg-WT fibers (P < 0.01), indicating that the SL dependency of myofilament Ca(2+) sensitivity was blunted in Tg-Δ43 fibers. The SL dependency of cross-bridge (XB) detachment kinetics was also blunted in Tg-Δ43 fibers because the decrease in XB detachment kinetics was significant (P < 0.001) only at SL 1.9 μm. Thus the increased XB dwell time at the short SL augments Ca(2+) sensitivity at short SL and thus blunts SL-mediated increase in myofilament Ca(2+) sensitivity. Our data suggest that the NH(2)-terminal extension of cardiac ELC not only augments the amplitude of force generation, but it also may play a role in mediating the SL dependency of XB detachment kinetics and myofilament Ca(2+) sensitivity.

Characterizations of myosin essential light chain’s N-terminal truncation mutant Δ43 in transgenic mouse papillary muscles by using tension transients in response to sinusoidal length alterations

“…The authors used muscle strips from 7 month old female Tg-WT and Tg-Δ43 mice, the same mouse models used in the current report. In agreement with the original study (Kazmierczak et al 2009) and the current investigation on Tg-Δ43 mice, Micheal et al (Michael et al 2012) showed that the deletion of 1-43 amino acids in cardiac ELC leads to impaired tension development and decreased instantaneous stiffness parameter ( E D ) that is a measure of the muscle fibre stiffness due to the strain of strongly-bound cross-bridges. They concluded that a decrease in E D in Tg-Δ43 fibres is due to a decrease in the number of strongly-bound cross-bridges in Tg-Δ43 mice, the same conclusion that was reached in the current report.…”

“…Our data on stiffness and tension are in accord with those by Micheal et al (Michael et al 2012) published during the revision process of this manuscript . The authors used muscle strips from 7 month old female Tg-WT and Tg-Δ43 mice, the same mouse models used in the current report.…”

Discrete effects of A57G-myosin essential light chain mutation associated with familial hypertrophic cardiomyopathy

“…As we predicted earlier, the A57G mutation is anticipated to influence the local conformation of the ELC and interfere with the function of myosin lever arm to produce force (40). Considering its Ca 2ϩ -sensitizing effect on muscle contraction, it is likely that the A57G mutated N-terminal-ELC extension can directly communicate with the actin-Tm-Tn regulatory system (24,36). Noteworthy, in agreement with the model of Ca 2ϩ -dependent regulation of contraction proposed by McKillop and Geeves (34), we showed that myosin cross bridges can directly affect the Ca 2ϩ -dependent regulation of force development in the heart (15).…”

“…A wealth of evidence suggests that it may play a role in force development and muscle contraction (17,24,36,40,54). The functional importance of myosin ELC in cardiac muscle has emerged through the identification of several mutations in the ELC gene (MYL3) shown to cause familial hypertrophic cardiomyopathy (FHC).…”

Ventricular myosin modifies in vitro step-size when phosphorylated

“…Relative frequencies of the 3 and 5 nm steps are very different making it unlikely that they are sub-steps of the longer 8 nm unitary step. Cardiac myosin ELC’s (cELC, genes MYL3 or MYL4) have a unique N-terminus known to bind actin and to influence myosin function in the heart (14, 24, 25). Fast skeletal myosin ELC (MYL1) corresponds to either long (LC1) or short (LC3) ELC on sHMM with LC1 probably making an actin contact but unlike the binding of cELC (26).…”