Characterization of an ATP-binding cassette transporter in Cryptosporidium parvum

Cloning and Iron Transportation of Nucleotide Binding Domain of Cryptosporidium andersoni ATP-Binding Cassette (CaABC) Gene

Cryptosporidium andersoni ATP-binding cassette (CaABC) is an important membrane protein involved in substrate transport across the membrane. In this research, the nucleotide binding domain (NBD) of CaABC gene was amplified by PCR, and the eukaryotic expression vector of pEGFP-C1-CaNBD was reconstructed. Then, the recombinant plasmid of pEGFP-C1-CaNBD was transformed into the mouse intestinal epithelial cells (IECs) to study the iron transportation function of CaABC. The results indicated that NBD region of CaABC gene can significantly elevate the transport efficiency of Ca²⁺, Mg²⁺, K⁺, and HCO₃^- in IECs (P<0.05). The significance of this study is to find the ATPase inhibitors for NBD region of CaABC gene and to inhibit ATP binding and nutrient transport of CaABC transporter. Thus, C. andersoni will be killed by inhibition of nutrient uptake. This will open up a new way for treatment of cryptosporidiosis.

Comparative genome analysis of two Cryptosporidium parvum isolates with different host range

Parasites of the genus Cryptosporidium infect the intestinal and gastric epithelium of different vertebrate species. Some of the many Cryptosporidium species described to date differ with respect to host range; whereas some species' host range appears to be narrow, others have been isolated from taxonomically unrelated vertebrates. To begin to investigate the genetic basis of Cryptosporidium host specificity, the genome of a Cryptosporidium parvum isolate belonging to a sub-specific group found exclusively in humans was sequenced and compared to the reference C. parvum genome representative of the zoonotic group. Over 12,000 single-nucleotide polymorphisms (SNPs), or 1.4 SNP per kilobase, were identified. The genome distribution of SNPs was highly heterogeneous, but non-synonymous and silent SNPs were similarly distributed. On many chromosomes, the most highly divergent regions were located near the ends. Genes in the most diverged regions were almost twice as large as the genome-wide average. Transporters, and ABC transporters in particular, were over-represented among these genes, as were proteins with predicted signal peptide. Possibly reflecting the presence of regulatory sequences, the distribution of intergenic SNPs differed according to the function of the downstream open reading frame. A 3-way comparison of the newly sequenced anthroponotic C. parvum, the reference zoonotic C. parvum and the human parasite Cryptosporidium hominis identified genetic loci where the anthroponotic C. parvum sequence is more similar to C. hominis than to the zoonotic C. parvum reference. Because C. hominis and anthroponotic C. parvum share a similar host range, this unexpected observation suggests that proteins encoded by these genes may influence the host range.

P-glycoprotein inhibitors modulate accumulation and efflux of xenobiotics in extra and intracellular Toxoplasma gondii

We examined xenobiotic transport and the effects of P-glycoprotein (Pgp) inhibitors on efflux function in Toxoplasma gondii tachyzoites. The fluorescence emission of JC-1 and daunorubicin (Pgp substrates) was determined in both extracellular tachyzoites and T. gondii-infected human KB cells. Dye accumulation and efflux were modulated by verapamil (Vp) and cyclosporin A (CsA), both of which are Pgp inhibitors. Red JC-1 emission was measured from 10(6) extracellular tachyzoites, using spectrofluorometry. The increase in red emission was significant from 1 microM concentration of both drugs and was higher with CsA than with Vp. Compared with untreated tachyzoites, JC-1 efflux was inhibited by 3 microM CsA and 3 microM Vp. With intracellular tachyzoites, the fluorescence distribution of daunorubicin (DNR) between the parasitophorous vacuole and the host cell was modulated by Vp and CsA. In media free of CsA and Vp, DNR emission inside intracellular tachyzoites was very weak, as observed by confocal microscopy. In the presence of CsA or Vp, DNR emission was markedly enhanced in tachyzoites but not in the whole vacuole. The modulation of DNR uptake seems to involve the tachyzoite membrane rather than the parasitophorous vacuole or host cell membranes. It suggests that Vp would inhibit the DNR efflux from intracellular tachyzoites through a transitory effect. In conclusion, these two Pgp inhibitors increase both extracellular and intracellular dye accumulation in living T. gondii, pointing to the existence of a transmembrane transport mediated by a Pgp homologue located on the parasite membrane complex.

Cryptosporidiosis and the challenges of chemotherapy

Cryptosporidium parvum is a protozoan parasite that infects the epithelial cells of the small intestine causing diarrheal illness in humans. Cryptosporidium has a worldwide distribution and is considered an emerging zoonosis. Despite intensive efforts to develop workable experimental models, and the evaluation of over 200 chemotherapeutic agents, adequate therapies to clear the host of these parasites are still lacking. The reasons for the lack of drug efficacy are probably manifold and may include the unusual location of the parasite in the host cell, distinct structural and biochemical composition, or its ability to either block import or rapidly efflux drug molecules. Understanding some of the basic mechanisms by which drugs are transported to the parasite and identifying unique targets is a first step in developing effective therapeutic agents.

CpABC, a Cryptosporidium parvum ATP-binding cassette protein at the host-parasite boundary in intracellular stages

The intracellular parasite Cryptosporidium parvum develops inside a vacuole at the apex of its epithelial host cell. The developing parasite is separated from the host cell cytoplasm by a zone of attachment that consists of an extensively folded membranous structure known as the feeder organelle. It has been proposed that the feeder organelle is the site of regulation of transport of nutrients and drugs into the parasite. In this report, we localize an approximately 200-kDa integral membrane protein, CpABC, from Cryptosporidium parvum to the host-parasite boundary, possibly the feeder organelle. The predicted amino acid sequence of CpABC has significant structural similarity with the cystic fibrosis conductance regulator and the multidrug resistance protein subfamily of ATP-binding cassette proteins. This is an example of a parasite-encoded transport protein localized at the parasite-host interface of an intracellular protozoan.

Establishing the Cryptosporidium parvum karyotype by NotI and SfiI restriction analysis and Southern hybridization

The molecular karyotype of the coccidian parasite Cryptosporidium parvum has proven difficult to study because chromosomes of similar sizes migrate together when submitted to pulsed-field gel electrophoresis (PFGE). In the present work, the karyotype was studied by restriction of chromosome-sized DNA with the rare-cutting enzymes NotI and SfiI, followed by PFGE separation of the restriction fragments and Southern hybridization. These experiments showed that the C. parvum karyotype is formed by eight chromosomes, ranging in size from approximately 0.95 to 1.45 million base pairs (Mbp), accounting for a genome size of 9.6Mbp. As a first step towards the construction of a physical map of the C. parvum genome, a total of 20 probes, including 16 genes and the ribosomal DNA (rDNA) sequence, was mapped to intact chromosomes and to their restriction fragments. In this way, all chromosomes, but one, were identified by specific markers. A comparison of mapping data of homologous genes from different species belonging to the phylum Apicomplexa showed differences in the distribution of rDNA sequences and in the chromosomal localization of alpha- and beta-tubulin genes. The variation in genome size among these parasites is also discussed.

Cyclosporin analogs inhibit in vitro growth of Cryptosporidium parvum

Cyclosporine and nonimmunosuppressive cyclosporin (CS) analogs were demonstrated to be potent inhibitors of the growth of the intracellular parasite Cryptosporidium parvum in short-term (48-h) in vitro cultures. Fifty-percent inhibitory concentrations (IC50s) were 0.4 microM for SDZ 033-243, 1.0 microM for SDZ PSC-833, and 1.5 microM for cyclosporine. Two other analogs were less effective than cyclosporine: the IC50 of SDZ 205-549 was 5 microM, and that of SDZ 209-313 was 7 microM. These were much lower than the IC50 of 85 microM of paromomycin, a standard positive control for in vitro drug assays for this parasite. In addition, intracellular growth of excysted sporozoites that had been incubated for 1 h in cyclosporine was significantly reduced, suggesting that the drug can inhibit sporozoite invasion. The cellular activities of the CS analogs used have been characterized for mammalian cells and protozoa. The two analogs that were most active in inhibiting C. parvum, SDZ PSC-833 and SDZ 033-243, bind weakly to cyclophilin, a peptidyl proline isomerase which is the primary target of cyclosporine and CS analogs. However, they are potent modifiers of the activity of the P glycoproteins/ multidrug resistance (MDR) transporters, members of the ATP-binding cassette (ABC) superfamily. Hence, both cyclophilin and some ABC transporters may be targets for this class of drugs, although drugs that preferentially interact with the latter are more potent. Cyclosporine (0.5 microM) had no significant chemosensitizing activity. That is, it did not significantly increase sensitivity to paromomycin, suggesting that an ABC transporter is not critical in the efflux of this drug. Cyclosporine at concentrations up to 50 microM was not toxic to host Caco-2 cells in the CellTiter 96 assay. The results of this study complement those of studies of the inhibitory effect of cyclosporine and CS analogs on other apicomplexan parasites, Plasmodium falciparum, Plasmodium vivax, and Toxoplasma gondii.

Ribosomal RNA gene organization in Cryptosporidium parvum

The cytoplasmic ribosomal RNA (rRNA) genes of the Apicomplexan protozoan parasite Cryptosporidium parvum have been analyzed with respect to size, copy number, organization and structure. The small and large subunit rRNAs are 1.7 and 3.6 kb, respectively. A 151 bp putative 5.8S rRNA gene was identified. The rDNA unit is 5' small subunit rRNA internal transcribed spacer 1-5.8S rRNA-internal transcribed spacer 2-large subunit rRNA 3'. There are five copies of the rDNA unit per haploid genome and they are not organized in a conventional head to tail tandem array with a conserved external transcribed spacer. The rDNA units are dispersed through the genome to at least three chromosomes. At least two of the rDNA units are single unlinked copies on different chromosomes. There are two structurally distinct types of rDNA unit, Type A and B, with marked differences in the internal transcribed spacer regions. There are four copies of the Type A rDNA unit and one copy of the Type B rDNA unit.