The intracellular parasite Toxoplasma gondii contains a structure known as the microneme (a secretory organelle) at its apical end. The microneme is needed for parasite invasion and is thought to provide components required for binding to host cells and for the formation of the parasitophorous vacuole, in which the parasite grows and replicates.
Reiss et al. have discovered that the biogenesis of micronemal proteins involves helpers that mediate the transport and targeting of newly synthesized protein to the growing organelle. The transmembrane protein MIC6 acts as an escort for two soluble micronemal proteins, MIC1 and MIC4, by forming a tripartite complex within the endoplasmic reticulum, followed by transit to the microneme. Both MIC1 and MIC4 are adhesins that likely participate in binding to host membranes. Taken together their findings suggest that the three-component complex may act as a bridge between the invading parasite and the host cell. -- SMH
J. Cell Biol. 152, 563 (2001).
