Identification and localization of proteins in gregarines that are immunologically related to smooth muscle α-actinin

Abstract

Summary The immunological cross-reactivity of proteins from gregarine cell extracts with polyclonal and monoclonal antibodies against smooth muscle α-actinin was demonstrated by immunoblotting in one- and two dimensional gel electrophoresis and by immunofluorescence microscopy. In immunoblotting, two proteins of Gregarina blaberae with Mr = 90,000 and Mr = 66,000 and with isoelectric points of 5.5 and 5.9, respectively, showed cross-reactivity with anti-α-actinin antibodies. Electrophoretic analysis showed that the two proteins were associated with ghosts and a cytoplasmic extract of trophozoite and sexual stages. The Mr = 90,000 and the Mr = 66,000 proteins were extracted from G. blaberae ghosts by 6 M urea in high ionic strength buffer. Indirect immunofluorescence antibody staining showed these polypeptides to be localized in the cell cortex, within longitudinal lines underlying the folds of G. blaberae (Polycystidae) and Lecudina pellucida (Monocystidae), and with lines separating the large folds of Selenidium pendula (Selenidiidae). The presence of two distinct forms (Mr = 90,000 and Mr = 66,000) of α-actinin is discussed with regard to the motility of gregarines.