Mitochondrial-type iron-sulfur cluster biosynthesis genes (IscS and IscU) in the apicomplexan Cryptosporidium parvum

1 Wadsworth Center, New York State Department of Health, PO Box 22002, Albany, NY 12201-2002, USA 2 First Faculty of Medicine, Charles University, Prague, Czech Republic 3 Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic Correspondence Michael J. LaGier michael.lagier{at}noaa.gov Several reports have indicated that the iron–sulfur cluster [Fe–S] assembly machinery in most eukaryotes is confined to the mitochondria and chloroplasts. The best-characterized and most highly conserved [Fe–S] assembly proteins are a pyridoxal-5'-phosphate-dependent cysteine desulfurase (IscS), and IscU, a protein functioning as a scaffold for the assembly of [Fe–S] prior to their incorporation into apoproteins. In this work, genes encoding IscS and IscU homologues have been isolated and characterized from the apicomplexan parasite Cryptosporidium parvum , an opportunistic pathogen in AIDS patients, for which no effective treatment is available. Primary sequence analysis (CpIscS and CpIscU) and phylogenetic studies (CpIscS) indicate that both genes are most closely related to mitochondrial homologues from other organisms. Moreover, the N-terminal signal sequences of CpIscS and CpIscU predicted in silico specifically target green fluorescent protein to the mitochondrial network of the yeast Saccharomyces cerevisiae . Overall, these findings suggest that the previously identified mitochondrial relict of C. parvum may have been retained by the parasite as an intracellular site for [Fe–S] assembly. Abbreviations: BP, bootstrap proportion; [Fe–S], iron–sulfur cluster(s); GFP, green fluorescent protein; gDNA, genomic DNA; ML, maximum-likelihood; MP, maximum-parsimony; NJ, neighbour-joining; P , probability score; PLP, pyridoxal 5'-phosphate Present address: University of Miami, CIMAS, 4600 Rickenbacker Causeway, Miami, FL 33149, USA. The GenBank accession numbers for the sequences reported in this paper are AY029212 ( CpIscS ) and AY078500 ( CpIscU ).