Abstract
Background information: Toxoplasma gondii is among the most successful parasites, with nearly half of the human population chronically infected. T. gondii has 5 small heat shock (sHsp) proteins located in different subcellular compartments. Among them, Hsp20 showed to be localized at the periphery of the parasite body. sHsps are widespread, constituting the most poorly conserved family of molecular chaperones. The presence of sHsps in membrane structures is unusual. Results: The localization of Hsp20 was further analyzed using high resolution fluorescent light microscopy as well as electron microscopy, which revealed that Hsp20 is associated to the outer surface of the inner membrane complex (IMC), in a set of discontinuous stripes following the same spiraling trajectories as the subpellicular microtubules. Detergent extraction profile of Hsp20 was similar to that of GAP45, a glideosome protein associated to inner membrane complex (IMC), but different from that of IMC1 protein. Although we were unable to detect interacting protein partners of Hsp20 either in normal or stressed tachyzoites, an interaction of Hsp20 with phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5 biphosphate phospholipids could be observed. Conclusions: Hsp20 showed to be associated to a specialized membranous structure of the parasite, the IMC. This discontinuous striped-arrangement is unique in T. gondii, indicating that the topology of the outer leaflet of the IMC is not homogeneous.