Enolase from Trypanosoma brucei, from the amitochondriate protist Mastigamoeba balamuthi, and from the chloroplast and cytosol of Euglena gracilis: Pieces in the evolutionary puzzle of the eukaryotic glycolytic pathway

Genomic or cDNA clones for the glycolytic enzyme enolase were isolated from the amitochondriate pelobiont Mastigamoeba balamuthi, from the kinetoplast id Trypanosoma brucei, and from the euglenid Euglena gracilis. Clones for t he cytosolic enzyme were found in all three organisms, whereas Euglena was found to also express mRNA for a second isoenzyme that possesses a putative N-terminal plastid-targeting peptide and is probably targeted to the chlor oplast. Database searching revealed that Arabidopsis also possesses a secon d enolase gene that encodes an N-terminal extension and is likely targeted to the chloroplast. A phylogeny of enolase amino acid sequences from 6 arch aebacteria, 24 eubacteria, and 32 eukaryotes showed that the Mastigamoeba e nolase tended to branch with its homologs from Trypanosoma and from the ami tochondriate protist Entamoeba histolytica. The compartment-specific isoenz ymes in Euglena arose through a gene duplication independent of that which gave rise to the compartment-specific isoenzymes in Arabidopsis, as evidenc ed by the finding that the Euglena enolases are more similar to the homolog from the eubacterium Treponema pallidum than they are to homologs from any other organism sampled. In marked contrast to all other glycolytic enzymes studied to date, enolases from all eukaryotes surveyed here (except Euglen a) are not markedly more similar to eubacterial than to archaebacterial hom ologs. An intriguing indel shared by enolase from eukaryotes, from the arch aebacterium Methanococcus jannaschii, and from the eubacterium Campylobacte r jejuni maps to the surface of the three-dimensional structure of the enzy me and appears to have occurred at the same position in parallel in indepen dent lineages.