Biomechanics, Muscle Fibers, and How to Interface Experimental Apparatus to a Computer by Masataka Kawai

Author:Masataka Kawai
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

4.12 Ionic Interaction

On approach of myosin to the actin in the thin filament, the first force experienced by these molecules is ionic interaction. This is because the ionic interaction works over a long distance (~7Å at physiological IS (Wang et al., 2015)). This interaction is also called “electrostatic interaction,” because force develops between two charged groups. It is also called “Coulombic interaction” after Charles-Augustin de Coulomb who formulated this force (Coulomb, 1785). Myosin’s loop 2 has 5 positively charged Lys residues, and actin’s N-terminal has four negatively charged residues Asp and Glu. It has been thought that electrostatic interaction between these two groups of residues is essential for the initial actomyosin interaction. The significance of these groups was first demonstrated in cross-linked actin and myosin (Sutoh, 1983), and later with a loop 2 mutant of myosin’s motor domain (Furch et al., 1998), both in solution systems. We have shown their importance in the skinned fibre system, where the thin filament was extracted and reconstituted (Sect. 4.16) with yeast-generated mutant forms of actin, in which N-terminal negative charges were of variable length (Lu et al., 2005). Skinned fibre studies are important because all the contractile proteins are present at high concentrations in the presence of steric constraints and cooperativity among constituent proteins, experiments can be performed under the physiological ionic conditions that exist in working myocytes, and active force is measured.

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