MOLECULAR CHARACTERIZATION OF THE ENOLASE GENE FROM THE HUMAN MALARIAPARASITE PLASMODIUM-FALCIPARUM - EVIDENCE FOR ANCESTRY WITHIN A PHOTOSYNTHETIC LINEAGE

We have isolated and characterised the gene encoding the glycolytic en zyme enolase (2-phos- pho-D-glycerate hydrolase) from the human malari a parasite Plasmodium falciparum. This was achieved using a combinatio n of cDNA sequencing and inverse-PCR techniques. The gene maps to chro mosome 10 of the parasite. We have also mapped two further glycolytic enzyme genes, glyceraldehyde-3-phosphate dehydrogenase and triose-phos phate isomerase, to chromosome 14. The enolase gene encodes a protein of 446 amino acids (48.7 kDa), and all amino acid residues implicated in substrate/cofactor binding and catalysis are conserved in the malar ial enolase molecule. The predicted protein sequence displays approxim ately 60-70% identity to enolase molecules of other eukaryotes, the cl osest relationship with its homologues seen amongst the seven fully de scribed glycolytic pathway enzymes of P. falciparum. Of particular sig nificance in this well conserved molecule is a characteristic 5-amino- acid insertion sequence that is identical in position and virtually id entical in primary structure to that which is otherwise found uniquely in plant enolase proteins. This pentapeptide, together with other fea tures of the plasmodial sequence, points to a common ancestry with pho tosynthetic organisms at the level of a protein-encoding nuclear gene, thus extending earlier analyses of nuclear small-subunit ribosomal RN A genes, and of an extrachromosomal circular 35-kb DNA element found i n P. falciparum, which have also indicated such a relationship.