Fig. 4. MTIP localizes to the inner membrane complex of Plasmodium sporozoites and co-localizes with MyoA. (A) The transmission electron micrograph of a longitudinal sporozoite section shows the architecture of the sporozoite cortex. The trilaminar pellicle consists of the plasma membrane (white arrow) and the IMC (black arrow) separated by the cortical cytoplasm. m, micronemes; mt, microtubules. (B) Immunoelectron microscopy of sporozoite sections labeled with anti-MTIP (15 nm gold particles). MTIP localized to the periphery of sporozoites and showed circumferential distribution. Almost no labeling was observed in the internal cytoplasm. The gold particles decorated an electron dense structure located 15 nm internal to the presumed plasma membrane. The position of gold particles is consistent with an IMC localization of MTIP. (C,D) Sporozoite sections double-labeled with anti-MyoA (5 nm gold particles) and anti-MTIP (15 nm gold particles) localized both proteins to the periphery of the sporozoite. MTIP was frequently clustered with MyoA. (E,F) Cryo-immunoelectron microscopy localized MTIP (10 nm gold particles) to the inner membrane complex and cortical cytoplasm of sporozoites. Note the absence of plasma membrane and the persistence of MTIP labeling in some positions. The white arrow indicates the plasma membrane; the black arrow indicates the IMC. The inset in F shows the apical prominence of a sporozoite. No gold particles label the prominence beyond the termination points of the IMC.