Characterization of Myosin-A and Myosin-C: Two class XIV unconventional myosins from Toxoplasma gondii

Two class XIV unconventional myosins from Toxoplasma gondii, Myosin-A (TgM- A) and Myosin-C (TgM-C), were characterized in terms of their biochemical p roperties and their expression in quiescent and motile stages of the parasi te life cycle. In cell fractionation studies, both myosins partitioned with the major organelle/cell membrane fraction, and extraction studies indicat ed that both were tightly associated with membrane domains as detergent was necessary for their solubilization. In addition, both TgM-A and TgM-C demo nstrated a hallmark feature of myosins in their ability to bind actin in th e absence but not the presence of ATP. In parasites residing within the hos t cell parasitdphorous vacuole, TgM-A was detected by immunofluorescence mi croscopy as a bright spot near the apical pole of the parasite. This patter n underwent a subtle change as the parasites became motile, with TgM-A then localizing more intimately with the parasite cell membrane domain in apica lly disposed spots or patches, consistent with the role of this myosin in g liding motility. TgM-C showed a distinct localization to the juxtanuclear r egion towards the epical pale of the parasite, consistent with an associati on with the Golgi apparatus. (C) 1999 Wiley-Liss, Inc.