Identification, characteristic and phylogenetic analysis of type II DNA topoisomerase gene in Giardia lamblia

Abstract

The genes encoding type II DNA topoisomerases were investigated in Giardia lamblia genome, and a type IIA gene, GlTop 2 was identified. It is a single copy gene with a 4476 bp long ORF without intron. The deduced amino acid sequence shows strong homology to eukaryotic DNA Top 2. However, some distortions were found, such as six insertions in the ATPase domain and the central domain, a ~100 aa longer central domain; a ~200 aa shorter C-terminal domain containing rich charged residues. These features revealed by comparing with Top 2 of the host, human, might be helpful in exploiting drug selectivity for antigiardial therapy. Phylogenetic analysis of eukaryotic enzymes showed that kinetoplastids, plants, fungi, and animals were monophyletic groups, and the animal and fungi lineages shared a more recent common ancestor than either did with the plant lineage; microsporidia grouped with fungi. However, unlike many previous phylogenetic analyses, the "amitochondriate" G. lamblia was not the earliest branch but diverged after mitochondriate kinetoplastids in our trees. Both the finding of typical eukaryotic type IIA topoisomerase and the phylogenetic analysis suggest G. lamblia is not possibly as primitive as was regarded before and might diverge after the acquisition of mitochondria. This is consistent with the recent discovery of mitochondrial remnant organelles in G. lamblia.

DNA Topoisomerase II Is Involved in Regulation of Cyst Wall Protein Genes and Differentiation in Giardia lamblia

“…We first focused on understanding the role of topoisomerase II (Topo II) in Giardia . This Topo II has been reported previously [56]. Comparison of genomic and cDNA sequences showed that the topo II gene contained no introns.…”

“…A putative topoisomerase II (Topo II) has been identified in G. lamblia genome [56]. During encystation, a trophozoite may differentiate into a cyst by dividing 2 nuclei and by replicating DNA, generating a cyst with 4 nuclei [1].…”

Drug Target Identification in Intracellular and Extracellular Protozoan Parasites

“…It is, however, unclear, which type of enzyme is inhibited. A phylogenetic analysis of type II topoisomerases showed that the gene coding for the G. lamblia topoisomerase 2 (GlTop2) is eukaryote-like and thus not closely related to prokaryote topoisomerases [24]. Moreover, fluoroquinolones are effective against some apicomplexans including T. gondii most probably due to interference with the prokaryote type of translation that takes place in the apicoplast [25].…”

Identification and evolutionary implication of four novel box H/ACA snoRNAs from Giardia lamblia

“…Therefore, Giardia is previously regarded as a missing link between prokaryotes and eukaryotes [25] . Although the evolutionary position of G. lamblia has been challenged by recent researches and some biologists suggest that it is possibly not the most primitive eukaryote [26][27][28][29] , G. lamblia undoubtedly represents an important primitive eukaryotic model for the study of biological evolutions. Previously, we have primarily investigated the snoRNAs in G. lamblia and found that the G. lamblia snoRNAs have unique features different from the counterparts previously identified from Archaea and other unicellular protozoan in gene structures, functions, genomic organizations and expression models [30] .…”