Functional characterization of GAP50: the integral membrane receptor for the myosin motor complex in Toxoplasma gondii Public Deposited

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  • March 21, 2019
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  • Johnson, Terezina Marie
    • Affiliation: School of Medicine, Department of Cell Biology and Physiology
Abstract
  • Toxoplasmosis is a serious disease caused by the obligate intracellular parasite Toxoplasma gondii. Lacking locomotive organelles such as flagellae, these parasites exhibit a unique substrate-dependent motion called gliding motility. Detailed studies in Toxoplasma and the closely related malarial agent, Plasmodium, have revealed that gliding motility is required for survival throughout many stages of the life cycle, including host cell invasion and egress. Although it has been demonstrated that parasite motility requires an active actin-myosin motility system, the structure and regulation of this system are not known in any detail (Dobrowolski et al., 1997; Meissner et al., 2002; Wetzel et al., 2003). The myosin involved in Toxoplasma motility, TgMyoA, is found in a complex with myosin light chain (TgMLC1), TgGAP45 and TgGAP50, the membrane anchor for the complex (Gaskins et al., 2004). The overall goal of this research is to determine the functional attributes of the gliding motility complex in these parasites, known as the glideosome. Toxoplasma motility is likely to be regulated at the level of this complex, and the importance of these accessory proteins is now being discovered. This thesis will focus on two of the accessory proteins, TgGAP50 and TgGAP45 that accompany the driving myosin motor, TgMyoA. We have discovered that the TgMyoA anchor, TgGAP50, is immobilized in the outer face of the cholesterol-enriched inner membrane complex; a discovery that is fundamental to understanding the mechanism of force generation by TgMyoA. We have also determined that the lumenal domain and the first half of the transmembrane domain of TgGAP50 are required for targeting of the protein, while the cytoplasmic domain is necessary for glideosome formation and therefore, motility. Lastly, we have uncovered an unusual structural characteristic of TgGAP45, potentially revealing its function in motility, and have established a method for glideosome purification. These results shed light on basic cellular processes such as cell motility and may eventually reveal new targets for therapeutic interventions for diseases caused by parasites such as toxoplasmosis and malaria.
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  • Beckers, Cornelis J.
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