Actin and myosin-linked calcium regulation in the nematode Caenorhabditis elegans. Biochemical and structural properties of native filaments and purified proteins

Abstract

Calcium regulation of actomyosin activity in the nematode C. elegans was studied with purified proteins and crude thin filaments. Actin and tropomyosin were purified from C. elegans and shown to be similar in most respects to actin and tropomyosin from rabbit skeletal muscle. The actin comigrates with rabbit actin on polyacrylamide-sodium dodecyl sulfate gel electrophoresis, forms similar filaments and paracrystals and activates the Mg2+-ATPase of rabbit myosin heads as efficiently as rabbit actin. Nematode tropomyosin has a greater apparent molecular weight (estimated by mobility on polyacrylamide-sodium dodecyl sulfate gels) than the rabbit protein, yet it forms Mg2+-paracrystals with a slightly shorter periodicity. Native thin filaments extracted from nematodes activate rabbit myosin subfragment 1 Mg2+-ATPase in a Ca sensitive manner; the extent of activation is 3-fold greater in 0.2 mM CaCl2 than in the absence of Ca. The thin filaments probably contain components functionally equivalent to vertebrate troponins. Ca is required for maximal activation of the Mg2+-ATPase of purified nematode myosin by pure rabbit F-actin. C. elegans has both myosin and thin filament-linked Ca regulatory systems. The origin of the actin, tropomyosin and myosin from different tissues and the use of genetic analysis to answer questions about assembly and function in vivo are discussed.