IDENTIFICATION OF A NOVEL GIARDIA-LAMBLIA CYST WALL PROTEIN WITH LEUCINE-RICH REPEATS - IMPLICATIONS FOR SECRETORY GRANULE FORMATION AND PREOTEIN ASSEMBLY INTO THE CYST WALL

Giardia lamblia trophozoites, like most intestinal parasitic protozoa, undergo fundamental biological changes to survive outside the intesti ne of their mammalian host by differentiating into infective cysts. Th is complex process entails the coordinated production, processing, and transport of cyst wall constituents for assembly into a protective cy st wall. Yet, little is known about this process and the identity of c yst wall constituents. We previously identified a 26-kDa cyst wall pro tein, CWP1. In the present work, using monoclonal antibodies to cyst w all antigens, we cloned the gene that encodes a novel 39-kDa cyst wall protein, CWP2. Expression of CWP1 and CWP2 was induced during encysta tion with identical kinetics. Soon after synthesis, these two proteins combine to form a stable complex, which is concentrated within the en cystation-specific secretory granules before incorporation into the cy st wall. Both proteins contain five tandem copies of a 24-residue leuc ine-rich repeat, a motif implicated in protein-protein interactions. U nlike CWP1, CWP2 has an extremely basic 121-residue COOH-terminal exte nsion that might be involved in the sorting of these proteins to the s ecretory granules.