Binding of Actin Filaments to Connectin1

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Abstract
The binding of actin filaments to connectin, a muscle elastic protein, was investigated by means of turbidity and sedimentation measurements and electron microscopy. In the presence of less than 0.12 M KCI at pH 7.0, actin filaments bound to connection. Long actin filaments formed bundles. Short actin filaments also aggregated into irregular bundles or a meshwork, and were frequently attached perpendicularly to long bundles. The binding of F-actin to connectin was saturated at an equal weight ratio (molar ratio, 50 : 1) as determined by a cosedimentation assay. Larger amounts of sonicated short actin filaments appeared to bind to connectin than intact F-actin. Myosin S1-decorated actin filaments did not bind to connectin. The addition of S1 to connectin-induced actin bundles resulted in partial disaggregation. Thus, connectin does not appear to interfere with actin-myosin interactions, since myosin S1 binds to actin more strongly than connectin.