Mitochondrial-type hsp70 genes of the amitochondriate protists, Giardia intestinalis, Entamoeba histolytica and two microsporidians

Abstract

Genes encoding putative mitochondrial-type heat shock protein 70 (mit-hsp70) were isolated and sequenced from amitochondriate protists, Giardia intestinalis, Entamoeba histolytica, and two microsporidians, Encephalitozoon hellem and Glugea plecoglossi. The deduced mit-hsp70 sequences were analyzed by sequence alignments and phylogenetic reconstructions. The mit-hsp70 sequence of these four amitochondriate protists were divergent from other mit-hsp70 sequences of mitochondriate eukaryotes. However, all of these sequences were clearly located within a eukaryotic mitochondrial clade in the tree including various type hsp70 sequences, supporting the emerging notion that none of these amitochondriate lineages are primitively amitochodrial, but lost their mitochondria secondarily in their evolutionary past.

Fig. 1

Two signature motifs found in mit-hsp70 sequences of eukaryotes including amitochondriate protists and in homologous proteobacterial sequences. Amino acid residues within the originally defined motifs[27], GDAWV and YSPSQI, are shown in bold face characters. Position numbers for the H. sapiens mit-hsp70 sequence were shown above the alignment. Localization within cell compartments was shown in parentheses: Mit, mitochondria; Hyd, hydrogenosome; and Chl, chloroplasts.

Fig. 2

Phylogenetic tree of mit-hsp70 homologs using proteobacterial hsp70s as outgroups. The best tree obtained by the maximum likelihood analysis of protein phylogeny using the PROTML program is shown. The horizontal length of each branch is proportional to the estimated number of substitutions. Bootstrap proportions are attached to the internal branches; * denotes amitochondriate protists. Mit, mitochondria; and Hyd, hydrogenosome. Accession numbers of the sequences are shown in parentheses.