Mapping of the actomyosin interfaces

Insights into myosin regulatory and essential light chains: a focus on their roles in cardiac and skeletal muscle function, development and disease

The activity of cardiac and skeletal muscles depends upon the ATP-coupled actin-myosin interactions to execute the power stroke and muscle contraction. The goal of this review article is to provide insight into the function of myosin II, the molecular motor of the heart and skeletal muscles, with a special focus on the role of myosin II light chain (MLC) components. Specifically, we focus on the involvement of myosin regulatory (RLC) and essential (ELC) light chains in striated muscle development, isoform appearance and their function in normal and diseased muscle. We review the consequences of isoform switching and knockout of specific MLC isoforms on cardiac and skeletal muscle function in various animal models. Finally, we discuss how dysregulation of specific RLC/ELC isoforms can lead to cardiac and skeletal muscle diseases and summarize the effects of most studied mutations leading to cardiac or skeletal myopathies.

The cardiac myosin heavy chain Arg-403-->Gln mutation that causes hypertrophic cardiomyopathy does not affect the actin- or ATP-binding capacities of two size-limited recombinant myosin heavy chain fragments

Our aim was to investigate the potential functional consequences of myosin heavy chain (MHC) mutations identified in patients with familial hypertrophic cardiomyopathy. We observed the presence of a mutated beta-MHC mRNA in a formalin-fixed paraffin-embedded myocardial tissue of a proband from family A, which Geisterfer-Lowrance et al. [Geisterfer-Lowrance, Kass, Tanigawa, Vosberg, McKenna, Seidman and Seidman (1990) Cell 62, 999-1006] identified as carrying the Arg-403 to Gln mutation. Recombinant DNA methods were then used to obtain size-limited, soluble and undenatured fragments of mutated myosin subfragment 1 focused around the 403 mutation. The present analysis indicated that the 403 mutation did not quantitatively alter the actin- or ATP-binding capacities of two 246-residue or 524-residue-long recombinant MHC fragments containing this mutation. The absence of any apparent impact of the 403 mutation in the recombinant MHC fragments on interactions between actin and ATP is discussed in relation to numerous biochemical and structural reports which demonstrate the crucial role of the central MHC segment, where the 403 mutation occurs, in myosin functions.