Characterisation of a novel transporter from Cryptosporidium parvum

Differential Gene Expression and Protein Localization of Cryptosporidium parvum Fatty Acyl-CoA Synthetase Isoforms

Cryptosporidium parvum is unable to synthesize fatty acids de novo, but possesses three long-chain fatty acyl-CoA synthetase (CpACS) isoforms for activating fatty acids. We have recently shown that these enzymes could be targeted to kill the parasite in vitro and in vivo. Here, we demonstrated that the CpACS genes were differentially expressed during the parasite life cycle, and their proteins were localized to different subcellular structures by immunofluorescence and immuno-electron microscopies. Among them, CpACS1 displayed as an apical protein in sporozoites and merozoites, but no or little presence during the intracellular merogony until the release of merozoites, suggesting that CpACS1 probably functioned mainly during the parasite invasion and/or early stage of intracellular development. Both CpACS2 and CpACS3 proteins were present in all parasite life cycle stages, in which CpACS2 was present in the parasite and the parasitophorous vacuole membranes (PVM), whereas CpACS3 was mainly present in the parasite plasma membranes with little presence in the PVM. These observations suggest that CpACS2 and CpACS3 may participate in scavenging and transport of fatty acids across the PVM and the parasite cytoplasmic membranes, respectively.

Cryptosporidium pathogenicity and virulence

Cryptosporidium is a protozoan parasite of medical and veterinary importance that causes gastroenteritis in a variety of vertebrate hosts. Several studies have reported different degrees of pathogenicity and virulence among Cryptosporidium species and isolates of the same species as well as evidence of variation in host susceptibility to infection. The identification and validation of Cryptosporidium virulence factors have been hindered by the renowned difficulties pertaining to the in vitro culture and genetic manipulation of this parasite. Nevertheless, substantial progress has been made in identifying putative virulence factors for Cryptosporidium. This progress has been accelerated since the publication of the Cryptosporidium parvum and C. hominis genomes, with the characterization of over 25 putative virulence factors identified by using a variety of immunological and molecular techniques and which are proposed to be involved in aspects of host-pathogen interactions from adhesion and locomotion to invasion and proliferation. Progress has also been made in the contribution of host factors that are associated with variations in both the severity and risk of infection. Here we provide a review comprised of the current state of knowledge on Cryptosporidium infectivity, pathogenesis, and transmissibility in light of our contemporary understanding of microbial virulence.

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.

Cryptosporidium: genomic and biochemical features

Recent progress in understanding the unique biochemistry of the two closely related human enteric pathogens Cryptosporidium parvum and Cryptosporidium hominis has been stimulated by the elucidation of the complete genome sequences for both pathogens. Much of the work that has occurred since that time has been focused on understanding the metabolic pathways encoded by the genome in hopes of providing increased understanding of the parasite biology, and in the identification of novel targets for pharmacological interventions. However, despite identifying the genes encoding enzymes that participate in many of the major metabolic pathways, only a hand full of proteins have actually been the subjects of detailed scrutiny. Thus, much of the biochemistry of these parasites remains a true mystery.