Cryptosporidium parvum is one of the apicomplexans that can cause severe
diarrhea in humans and animals. The slow development of anti-
cryptosporidiosis chemotherapy is primarily due to the poor understanding on the basic metabolic pathways in this parasite. Many well-defined or promising
drug targets found in other apicomplexans are either absent or highly divergent in C. parvum. The recently discovered apicoplast and its associated Type II
fatty acid synthetic
enzymes in Plasmodium, Toxoplasma, and Eimeria apicomplexans are absent in C. parvum, suggesting this parasite is unable to synthesize
fatty acids de novo. However, C. parvum possesses a giant
Type I fatty acid synthase (CpFAS1) that makes very long chain
fatty acids using mediate or long chain
fatty acids as precursors. Cryptosporidium also contains a
Type I polyketide synthase (CpPKS1) that is probably involved in the production of unknown
polyketide(s) from a
fatty acid precursor. In addition to CpFAS1 and CpPKS1, a number of other
enzymes involved in
fatty acid metabolism have also been identified. These include a long chain fatty acyl elongase (LCE), a cytosolic
acetyl-CoA carboxylase (ACCase), three
acyl-CoA synthases (ACS), and an unusual "long-type"
acyl-CoA binding protein (ACBP), which allows us to hypothetically reconstruct the highly streamlined
fatty acid metabolism in this parasite. However, C. parvum lacks
enzymes for the oxidation of
fatty acids, indicating that
fatty acids are not an energy source for this parasite. Since
fatty acids are essential components of all biomembranes, molecular and functional studies on these critical
enzymes would not only deepen our understanding on the basic metabolism in the parasites, but also point new directions for the
drug discovery against C. parvum and other apicomplexan-based diseases.