Detection and localization of actin in Toxoplasma gondii

The immunological cross-reactivity of the protein from whole-cell extracts of Toxoplasma gondii with antisera against actins from chicken-gizzard smooth muscle and from Ascaris body-wall muscle was demonstrated by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis (SDS-PAGE) and immunofluorescence studies. A protein of about 42 kDa, with the same mobility as that of rabbit smooth-muscle actin in SDS-PAGE showed cross-reactivity with anti-actin antisera on the electroblotted nitrocellulose sheet. Indirect fluorescent antibody staining of the parasites clearly showed that actin localized strongly in the anterior third of the organism in both extra- and intrahost cellular stages. From both a biochemical as well as structural point of view, the results obtained in the present experiments might explain the locomotive features of the parasite such as twirling and sliding, with most of the activity at the anterior end.