Falcipain cysteine proteases require bipartite motifs for trafficking to the Plasmodium falciparum food vacuole

The Plasmodium falciparum cysteine proteases falcipain- 2 and falcipain- 3 hydrolyze hemoglobin in an acidic food vacuole to provide amino acids for erythrocytic malaria parasites. Trafficking to the food vacuole has not been well characterized. To study trafficking of falcipains, which include large membranespanning prodomains, we utilized chimeras with portions of the proteases fused to green fluorescent protein. The prodomains of falcipain- 2 and falcipain- 3 were sufficient to target green fluorescent protein to the food vacuole. Using serial truncations, deletions, and point mutations, we showed that both a 20-amino acid stretch of the lumenal portion and a 10-amino acid stretch of the cytoplasmic portion of the falcipain- 2 prodomain were required for efficient food vacuolar trafficking. Mutants with altered trafficking were arrested at the plasma membrane, implicating trafficking via this structure. Our results indicate that falcipains utilize a previously undescribed bipartite motif-dependent mechanism for targeting to a hydrolytic organelle, suggesting inhibition of this unique mechanism as a new means of antimalarial chemotherapy.