Molecular characterisation of the enolase gene from the human malaria parasite Plasmodium falciparum Evidence for ancestry within a photosynthetic lineage

Abstract

We have isolated and characterised the gene encoding the glycolytic enzyme enolase (2-phospho-D-glycerate hydrolase) from the human malaria parasite Plasmodium falciparum. This was achieved using a combination of cDNA sequencing and inverse-PCR techniques. The gene maps to chromosome 10 of the parasite. We have also mapped two further glycolytic enzyme genes, glyceraldehyde-3-phosphate dehydrogenase and triose-phosphate isomerase, to chromosome 14. The enolase gene encodes a protein of 446 amino acids (48.7 kDa), and all amino acid residues implicated in substratekofactor binding and catalysis are conserved in the malarial enolase molecule. The predicted protein sequence displays approximately 60-70% identity to enolase molecules of other eukaryotes, the closest relationship with its homologues seen amongst the seven fully described glycolytic pathway enzymes of R falciparum. Of particular significance in this well conserved molecule is a characteristic 5-amino-acid insertion sequence that is identical in position and virtually identical in primary structure to that which is otherwise found uniquely in plant enolase proteins. This pentapeptide, together with other features of the plasmodia1 sequence, points to a common ancestry with photosynthetic organisms at the level of a protein-encoding nuclear gene, thus extending earlier analyses of nuclear small-subunit ribosomal RNA genes, and of an extrachromosomal circular 35-kb DNA element found in I? falciparum, which have also indicated such a relationship.The glycolytic pathway has a number of features which suggest that it is particularly important to the blood-stage forms of the human malaria parasite Plasmodium falciparum, and thus make it an attractive candidate for experimental investigation. The level of glycolysis of parasite-infected cells is about 100-times greater than that observed in uninfected cells [l, 21 and can result in clinical hypoglycaemia as the infection progresses. ATP generation during this process is

Extrachromosomal DNA in the Apicomplexa

“…For example, an indel apparently characteristic of higher plants was found in the enolase gene of P. falciparum (89) while in an analysis of calmodulin, Robson et al (90) placed the malaria parasite in a monophyletic group with ciliates and plants. Similarly, the observation that the branch point for the malarial histone H2A gene in a dendrogram lay close to that of the pine tree (104) might be taken as another indication of a plant-like relationship.…”

Molecular Cloning of CTP: Phosphocholine Cytidylyltransferase from Plasmodium falciparum

“…More strikingly, recent cloning of the I? faleiparum enolase gene has described a pentapeptide insertion found uniquely in the higher plant homologues [51]. Unfortunately, a sufficient number of CCT sequences from the various species were not available to obtain informative points for the meaning of the insertion.…”

Sequence Variation of the Hydroxymethyldihydropterin Pyrophosphokinase: Dihydropteroate Synthase Gene in Lines of the Human Malaria Parasite, Plasmodium falciparum, with Differing Resistance to Sulfadoxine

“…In the glycolytic pathway, which is the best characterized metabolic pathway in the malaria parasite, at least four of the corresponding genes are located on a single chromosome [34]. It was thus of interest to determine on which of the 14 chromosomes the CH,OH-H,pterinPP kinase :H,Pte synthase gene was located, and whether it mapped to the same chromosome as the H,folate reductase :thymidylate synthase gene, which also encodes two activities in the folate pathway.…”