Molecular analysis of a Type I fatty acid synthase in Cryptosporidium parvum

We report here the molecular analysis of a Type I fatty acid synthase in the apicomplexan Cryptosporidium parvum (CpFAS1). The CpFAS1 gene encodes a multifunctional polypeptide of 8243 amino acids that contains 21 enzymatic domains. This CpFAS1 structure is distinct from that of mammalian Type I FAS, which contains only seven enzymatic domains. The CpFAS1 domains are organized into: (i) a starter unit consisting of a fatty acid ligase and an acyl carrier protein; (ii) three modules, each containing a complete set of six enzymes (acyl transferase, ketoacyl synthase, ketoacyl reductase, dehydrase, enoyl reductase, and acyl carrier protein) for the elongation of fatty acid C2-units; and (iii) a terminating domain whose function is as yet unknown. The CpFAS1 gene is expressed throughout the life cycle of C. parvum, since its transcripts and protein were detected by RT-PCR and immunofluorescent localization, respectively. This cytosolic Type I CpFAS1 differs from the organellar Type II FAS enzymes identified from Toxoplasma gondii and Plasmodium falciparum which are targetted to the apicoplast, and are sensitive to inhibition by thiolactomycin. That the discovery of CpFAS1 may provide a new biosynthetic pathway for drug development against cryptosporidiosis, is indicated by the efficacy of the FAS inhibitor cerulenin on the growth of C. parvum in vitro.