Putative SF2 helicases of the early-branching eukaryote Giardia lamblia are involved in antigenic variation and parasite differentiation into cysts

Abstract

BackgroundRegulation of surface antigenic variation in Giardia lamblia is controlled post-transcriptionally by an RNA-interference (RNAi) pathway that includes a Dicer-like bidentate RNase III (gDicer). This enzyme, however, lacks the RNA helicase domain present in Dicer enzymes from higher eukaryotes. The participation of several RNA helicases in practically all organisms in which RNAi was studied suggests that RNA helicases are potentially involved in antigenic variation, as well as during Giardia differentiation into cysts.ResultsAn extensive in silico analysis of the Giardia genome identified 32 putative Super Family 2 RNA helicases that contain almost all the conserved RNA helicase motifs. Phylogenetic studies and sequence analysis separated them into 22 DEAD-box, 6 DEAH-box and 4 Ski2p-box RNA helicases, some of which are homologs of well-characterized helicases from higher organisms. No Giardia putative helicase was found to have significant homology to the RNA helicase domain of Dicer enzymes. Additionally a series of up- and down-regulated putative RNA helicases were found during encystation and antigenic variation by qPCR experiments. Finally, we were able to recognize 14 additional putative helicases from three different families (RecQ family, Swi2/Snf2 and Rad3 family) that could be considered DNA helicases.ConclusionsThis is the first comprehensive analysis of the Super Family 2 helicases from the human intestinal parasite G. lamblia. The relative and variable expression of particular RNA helicases during both antigenic variation and encystation agrees with the proposed participation of these enzymes during both adaptive processes. The putatives RNA and DNA helicases identified in this early-branching eukaryote provide initial information regarding the biological role of these enzymes in cell adaptation and differentiation.

Resistance formation to nitro drugs in Giardia lamblia: No common markers identified by comparative proteomics

“…This is insofar interesting as this enzyme catalyzes the complete reduction and thus inactivation of nitro compounds in functional assays and in E. coli ( Müller et al, 2013 , 2015 ) and would therefore be a suitable candidate for up-regulation in resistant strains. Since the corresponding gene is transcribed in all strains ( Müller et al, 2013 ), either the mRNA is subjected to post-transcriptional gene silencing, most likely by RNA interference ( Prucca and Lujan, 2009 ; Gargantini et al, 2012 ) or the corresponding polypeptide is quickly degraded. We have performed immunoblots with specific antisera raised against two unique peptides of NR2 and could not detect a corresponding signal in G. lamblia trophozoite crude extracts (see Fig.…”

DEAD/DExH-Box RNA Helicases in Selected Human Parasites

“…A comparative genomic analysis of both Trypanosoma genomes showed that they display high levels of synteny and share a conserved set of approximately 6,200 genes [ 19 ]. Recently, Gargantini et al [ 20 ] identified a total of 103, 112, and 113 putative helicases in L. major , T. brucei , and T. cruzi genomes, respectively, from an extensive search in the TriTryp database. Interestingly, most predicted proteins are DEAD/DExH-box helicases with 27-30 members in the 3 species [ 15 ].…”

“…It has mitochondrial organelles called mitosomes [ 22 ] and 2 nuclei that contain 1.2×10 7 bp of DNA with a GC content of 46% [ 23 ]. From BLAST analyzes using the human eIF4A and DHX8 amino acid sequences as DEAD-box and DExH-box helicase prototypes, respectively, Gargantini et al [ 20 ] identified a set of 32 putative RNA helicases, including 22 DEAD-box and 6 DEAH-box proteins. G. lamblia proteins present high sequence similarity with characterized human and yeast homologs, which suggests that they may have a similar function in RNA metabolism.…”