Myosin and paramyosin of Caenorhabditis elegans: Biochemical and structural properties of wild-type and mutant proteins

Abstract

Myosin and paramyosin have been purified from the nematode, Caenorhabditis elegans. The properties of the myosin in general resemble those of other myosins. The native molecule is a dimer of heavy (210,000 dalton) polypeptide chains and contains 18,000 and 16,000 dalton light chains. When rapidly precipitated from solution, it forms small, bipolar aggregates, about 150 nm long, consistent with the expected molecular structure of a rigid rod with a globular head region at one end. Its ATPase activity is stimulated by CA 2+ and EDTA. The myosin binds to F actin in a polar and ATP-sensitive manner, and the Mg 2+-ATPase is activated by either F actin or nematode thin filaments. Dialysis of myosin to low ionic strength produces very long filaments. When a myosin-paramyosin mixture is dialyzed under the same conditions, co-filaments form which consist of a myosin cortex, surrounding a paramyosin core. Some properties of myosins from the mutants E675 and E190, which have functionally and structurally altered body wall muscles, are compared with those of wild-type myosin. These myosins behave normally in in vitro tests. The implications of these results are discussed in terms of the myosin heavy chain composition.