Cryptosporidium dense granule effector MUC5 interacts with host actin cytoskeleton through CD2AP

The parasite Cryptosporidium modulates the host cell cytoskeleton and microvilli during invasion and development. Identification of effector molecules and their targets is essential for understanding parasite-host interactions and pathogenesis. Here, we examined seven mucin glycoproteins (MUC1-MUC7) located on chromosome 2 of Cryptosporidium parvum using gene tagging. These small proteins are expressed in different secretory organelles including dense granules (DG), small granules (SG), and the rhoptry (ROP), and all but one are exported to the cytoplasm or microvilli of infected cells. Mutational studies of MUC5 revealed that its N-terminus contains a host cell targeting motif with a critical leucine residue at position 39. Immunoprecipitation and mutational studies showed that MUC5 interacts with the host cytoskeleton via its Px(P/A)xPR motifs and the SH3 domain of CD2AP. Deletion of MUC5 reduced the pathogenicity of a virulent isolate. These findings demonstrate the export of multiple Cryptosporidium DG and SG proteins into host cells and microvilli, and reveal a novel molecular mechanism by which Cryptosporidium effectors modulate the host cytoskeleton.