Structural and functional aspects of membranes and organelles of Trichomonas vaginalis.

Trichomonas vaginalis is a unicellular, flagellated, microaerophilic protozoan that extracellularly colonizes the human urogenital tract, causing trichomoniasis, a highly prevalent sexually transmitted infection (STI). This chapter explores the parasite's complex membrane structures and compositions, including the undulating membrane and its association with paracostal filaments and the costa. Key organelles such as the Golgi apparatus, lysosomes and hydrogenosomes are presented, detailing their structure, composition and biochemical activities. Unlike most eukaryotes, T. vaginalis lacks mitochondria, and instead, its hydrogenosomes are responsible for ATP synthesis, playing a critical role in the parasite's energy metabolism. The role of the plasma membrane in the endocytosis is addressed, alongside the involvement of the cytoskeleton and associated biochemical changes. Additionally, the chapter cover the parasite's interactions with host cells, focusing on the ameboid form of T. vaginalis. It emphasizes the morphological and structural transformations of the plasma membrane that occur during the transition from the piriform shape. Different types of vesicles associated with the plasma membrane, involved in host-parasite interactions, particularly their roles as adhesion molecules and in vesicular transport, are also discussed. The pseudocyst form of T. vaginalis, found under specific microenvironmental conditions, is also highlighted. In this form, the parasite internalizes its flagella, becoming rounded. The plasma membrane structure, composition and organelle modifications, as well as its relationship with host cells are highlighted. Furthermore, the implications of these transformations for the parasite's survival, immune evasion and pathogenic mechanisms are thoroughly reviewed, providing insights into how these membrane-associated adaptations enhance the parasite's pathogenicity.