Isolation and characterization of a high molecular weight actin-binding protein from Physarum polycephalum plasmodia.

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Abstract
A high MW actin-binding protein [HMWP] was isolated from the P. polycephalum plasmodia. HMWP shares many properties with other high MW actin-binding proteins such as spectrin, actin-binding protein from macrophages and filamin. It has a potent activity to cross-link F-actin into a gel-like structure. Its cross-linking activity does not depend on Ca concentrations. Hydrodynamic studies have revealed that the protein is in the monomeric state of a polypeptide chain with MW of .apprx. 230,000 in a high ionic strength solvent, while it self-associates into a dimer under physiological ionic conditions. EM of HMWP showed that the monomer particle observed in a high ionic strength solvent is rod shaped with the 2-stranded morphology very similar to that of spectrin. Under physiological ionic conditions, the HMWP dimer shows the dumb-bell shape with 2 globular domains connected with a thin flexible strand.