The possible role of myosin A1 light chain in the weakening of actin–myosin interaction

• Published in: Biochimica et biophysica acta Vol. 1340; no. 1; pp. 105 - 114
• Main Authors: St e ̧ pkowski, Dariusz, Efimova, Natalya, Paczyńska, Agnieszka, Moczarska, Anna, Nieznańska, Hanna, Kąkol, Irena
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.06.1997
• Subjects: Actin; Actins - metabolism; Actins - pharmacology; Adenosine Triphosphatases - metabolism; Animals; Binding Sites; Ca(2+) Mg(2+)-ATPase - metabolism; Calcium-Transporting ATPases - metabolism; Cation Transport Proteins; Kinetics; Myosin; Myosin alkali light chain; Myosin Light Chains - chemistry; Myosin Light Chains - physiology; Myosin Subfragments - metabolism; Myosins - metabolism; Osmolar Concentration; Papain - metabolism; Peptide Fragments - metabolism; Phosphorylation; Rabbits; Structure-Activity Relationship; Sulfhydryl Compounds - metabolism; Actin; Myosin alkali light chain; Myosin
• ISSN: 0167-4838; 0006-3002; 1879-2588
• DOI: 10.1016/S0167-4838(97)00031-9

The effects resulting from the removal of the N-terminus of myosin A1 by limited papain cleavage are investigated. The myosin and heavy meromyosin K +-ATPase and Ca 2+-ATPase activities, and actin-activated ATPase activity of heavy meromyosin (HMM) and subfragment-1, are studied. Myosin and HMM preparations devoid of the A1 N-terminus exhibits lower Ca 2+-ATPase activities at low ionic strength whereas no differences in K +- or Ca 2+-ATPase activities are observed at high ionic strength. Direct binding of actin to monomeric myosin under K +-activated ATPase conditions is much more effective for myosin containing a shortened A1 light chain. The kinetic constants K app for actin and V max are calculated from actin-activation curves for HMM and subfragment-1. The kinetic constants for HMM are determined under conditions assuring saturation of regulatory light chains (RLC) either with Mg 2+ or Ca 2+. The removal of the A1 N-terminus influences the actin–myosin interaction in a Ca 2+- and phosphorylation-dependent manner; in most cases, this leads to an increase in affinity. In the case of subfragment-1, the removal of the N-terminus of A1 led to a decrease in affinity. It is reasonable to assume that the intact A1 light chain may cause weakening of the actin–myosin interaction under certain conditions. This weakening may be regulated by RLC phosphorylation and RLC-bound calcium-for-magnesium exchange. Such an effect requires a structural minimum that is present in HMM but not in subfragment-1. Implications of such a role for the A1 N-terminus in the myosin–actin interaction are discussed.