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The lead enzymes of polyamine biosynthesis, i.e. ornithine decarboxylase (ODC) and arginine decarboxylase (ADC), were not detected in Toxoplasma gondii [the limit of detection for ODC and ADC was 5 pmol [min.sup.-1] [(mg protein).sup.-1]], indicating that T. gondii lacks a forward-directed polyamine biosynthetic pathway, and is therefore a polyamine auxotroph. The biochemical results were supported by results obtained from data-mining the T. gondii genome. However, it was possible to demonstrate the presence of a highly active backconversion pathway that formed spermidine from spermine, and putrescine from spermidine, via the combined action of spermidine/ spermine [N.sup.1]-acetyltransferase (SSAT) or spermidine [N.sup.1]-acetyltransferase (SAT) and polyamine oxidase (PAO). With spermine as the substrate, T. gondii SSAT had a specific activity of 1.84 nmol [min.sup.-1] [(mg protein).sup.-1], and an apparent [K.sub.m] for spermine of 180 mM; with spermidine as the substrate, the SAT had a specific activity of 3.95 nmol [min.sup.-1] [(mg protein).sup.-1], and a [K.sub.m] for spermidine of 240 mM. T. gondii PAO had a specific activity of 10.6 nmol [min.sup.-1] [(mg protein).sup.-1], and a [K.sub.m] for acetylspermine of 36 mM. Furthermore, the results demonstrated that T. gondii SSAT was 50 % inhibited by 30 mM di(ethyl)norspermine. The parasite actively transported arginine and ornithine, which were converted via the arginine dihydrolase pathway to citrulline and carbamoyl phosphate, resulting in the formation of ATP via carbamate kinase. The lack of polyamine biosynthesis by T. gondii is contrasted with polyamine metabolism by other apicomplexans.

Several reports have indicated that the iron-sulfur [Fe-S] assemblly machinery in most eukaryotes is confined to the mitochondria and chloroplasts. The best-characterised 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 (CplscS and CplscU) and phylogenetic studies (CplscS) indicate that both genes are most closely related to mitochondrial homologues from other organisms. Moreover, the N-terminal signal sequences of CplscS and CplscU 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.

The symptoms, diagnosis, treatment, and prevention of cryptosporidiosis are reviewed. This is a gastrointestinal infection with a parasite called Cryptosporidium. It causes diarrhea in healthy people, but can be much more serious in AIDS patients and other people with weakened immune systems.

Research has been conducted on the plastid genome. Results indicate that no genome has been found in Cryptosporidium parvum.

The S-adenosylhomocysteine hydrolase from the apicomplexan Cryptosporidium parvum ( CpSAHH) has been characterized. CpSAHH is a single-copy, intronless gene of 1479 bp encoding a protein of 493 amino acids with a molecular mass of 55.6 kDa. Reverse transcriptase-polymerase chain reaction analysis confirmed that CpSAHH is expressed both in intracellular stages (in C. parvum-infected HCT-8 cells 24 h after infection) and in sporozoites. CpSAHH was expressed in Escherichia coli TB1 cells as a fusion with maltose-binding protein. The recombinant fusion was cleaved by Factor Xa and the enzymatic activity of both the fusion protein and the purified separated CpSAHH was measured. The enzymatic activity of CpSAHH was inhibited byd-eritadenine, S-DHPA and Ara-A. [ABSTRACT FROM AUTHOR]

Cryptosporidium parvum contains a unique fusion protein pyruvate:NADP+ oxidoreductase ( CpPNO) that is composed of two distinct, conserved domains, an N-terminal pyruvate:ferredoxin oxidoreductase (PFO) and a C-terminal cytochrome P450 reductase (CPR). Unlike a similar fusion protein that localizes to the mitochondrion of the photosynthetic protist Euglena gracilis, CpPNO lacks an N-terminal mitochondrial targeting sequence. Using two distinct polyclonal antibodies raised against CpPFO and one polyclonal antibody against CpCPR, Western blot analysis has shown that sporozoites of C. parvum express the entire CpPNO fusion protein. Furthermore, confocal immunofluorescence and transmission electron microscopy confirm that CpPNO is localized within the cytosol rather than the relict mitochondrion of C. parvum. The distribution of this protein is not, however, strictly confined to the cytosol. CpPNO also appears to localize posteriorly within the crystalloid body. [ABSTRACT FROM AUTHOR]

Here we report a Narf-like gene from the apicomplexan Cryptosporidium parvum (CpNARF). CpNARF is an intronless, single-copy gene of 1680 bp which encodes a putative protein of 560 amino acids with a calculated molecular mass of 63.1 kDa. This gene contains a single highly conserved N-terminal iron–sulfur cluster ([4Fe–4S]) binding site, as well as most of the H-cluster conserved residues. Reverse transcription polymerase chain reaction analysis indicates that CpNARF is expressed by the intracellular stages of C. parvum. Although the function of this gene is as yet unknown, phylogenetic analyses suggest that CpNARF belongs to the group of NARF-like proteins from aerobic protists and higher eukaryotes, which are thought to have had an ancestor in common with [Fe]-hydrogenases. [Copyright &y& Elsevier]

The S-adenosylmethionine synthetase gene of the apicomplexan Cryptosporidium parvum (CpSAMS), an agent of diarrhea in immunocompromised and healthy humans and animals is described. CpSAMS is a single-copy, intronless gene of 1221 bp encoding a polypeptide of 406 amino acids with a molecular mass of 44.8 kDa. The gene is AT-rich (61.8%). CpSAMS was expressed in Escherichia coli TB1 cells as a fusion with maltose binding protein. The activity of the recombinant fusion was assayed, and was found to be inhibited by the methionine analog cycloleucine. In order to determine whether CpSAMS was differentially expressed during the life cycle of C. parvum, HCT-8 cells were infected with C. parvum and assayed over 72 h. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) confirmed the differential expression of CpSAMS. [Copyright &y& Elsevier]

Most eukaryotes perform the oxidative decarboxylation of pyruvate in mitochondria using pyruvate dehydrogenase (PDH). Eukaryotes that lack mitochondria also lack PDH, using instead the O2-sensitive enzyme pyruvate : ferredoxin oxidoreductase (PFO), which is localized either in the cytosol or in hydrogenosomes. The facultatively anaerobic mitochondria of the photosynthetic protist Euglena gracilis constitute a hitherto unique exception in that these mitochondria oxidize pyruvate with the O2-sensitive enzyme pyruvate : NADP oxidoreductase (PNO). Cloning and analysis of Euglena PNO revealed that the cDNA encodes a mitochondrial transit peptide followed by an N-terminal PFO domain that is fused to a C-terminal NADPH-cytochrome P450 reductase (CPR) domain. Two independent 5.8-kb full-size cDNAs for Euglena mitochondrial PNO were isolated; the gene was expressed in cultures supplied with 2% CO2 in air and with 2% CO2 in N2. The apicomplexan Cryptosporidium parvum was also shown to encode and express the same PFO-CPR fusion, except that, unlike E. gracilis, no mitochondrial transit peptide for C. parvum PNO was found. Recombination-derived remnants of PNO are conserved in the genomes of Saccharomyces cerevisiae and Schizosaccharomyces pombe as proteins involved in sulfite reduction. Notably, Trypanosoma brucei was found to encode homologs of both PFO and all four PDH subunits. Gene organization and phylogeny revealed that eukaryotic nuclear genes for mitochondrial, hydrogenosomal, and cytosolic PFO trace to a single eubacterial acquisition. These findings suggest a common ancestry of PFO in amitochondriate protists with Euglena mitochondrial PNO and Cryptosporidium PNO. They are also consistent with the view that eukaryotic PFO domains are biochemical relics inherited from a facultatively anaerobic, eubacterial ancestor of mitochondria and hydrogenosomes. [ABSTRACT FROM PUBLISHER]