We studied the properties of
actinogelin, a Ca2+-regulated actin cross-linking
protein isolated from Ehrlich
tumor cells or rat liver. Chicken gizzard
alpha-actinin was used as a Ca2+-insensitive control.
Actinogelin, which has very high gelation activity under low Ca2+ conditions, was found using electron microscopic or fluorescence studies to induce formation of a characteristic structure in which actin filaments and bundles radiate to (or converge from) all directions from spot-like core structures. A similar structure was induced with
actinogelin, even in the presence of 0.7 saturation of
tropomyosin. No such structure was detected with
actinogelin under high Ca2+ conditions, and only a few were found with gizzard
alpha-actinin. Because reconstituted structures are similar to those observed intracellularly,
actinogelin may be important in the formation of similar microfilament organization in the cells. It seems also important that these structures are reconstituted with only two purified
protein components, i.e.,
actinogelin and actin. Immunocompetition studies showed that
actinogelin and gizzard
alpha-actinin partially shared antigenicity, and their molecular shape and
peptide maps were similar. Their
amino acid compositions [Kuo et al., 1982], subunit and domain structures, and binding sites on actin [Mimura and Asano, 1987] are also very similar. Therefore, it is concluded that
actinogelin belongs to
alpha-actinin superfamily
proteins. Furthermore, the presence of functionally different subfamilies concerned with Ca2+ sensitivity, gelation-efficiency, and others is discussed.
Actinogelin, which induces networks of actin filaments, may be classified as high gelation type.