Giardia lamblia Expresses a Proteobacterial-like DnaK Homolog

Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
Molecular Biology and Evolution (Impact Factor: 9.11). 05/2001; 18(4). DOI: 10.1093/oxfordjournals.molbev.a003832
Source: OAI


We identified a novel gene encoding molecular chaperone HSP70 in the amitochondriate parasite Giardia lamblia. The predicted protein is similar to bacterial DnaK and mitochondrial HSP70s. The gene is transcribed and translated at a constant level during trophozoite growth and encystation. Alignment of the sequence with a data set of cytosolic, endoplasmic reticulum (ER), mitochondrial, and DnaK HSP70 homologs indicated that the sequence was extremely divergent and contained insertions unique to giardial HSP70s. Phylogenetic analyses demonstrated that this sequence was distinct from the cytosolic and ER forms and was most similar to proteobacterial and mitochondrial DnaKs. However, a specific relationship with the alpha proteobacterial and mitochondrial sequences was not strongly supported by phylogenetic analyses of this data set, in contrast to similar analyses of cpn60. These data neither confirm nor reject the possibility that this gene is a relic of secondary mitochondrial loss; they leave open the possibility that it was acquired in a separate endosymbiotic event.

Download full-text


Available from: Andrew J Roger, Feb 13, 2014
  • Source
    • "This cleavage could also be induced by some other adverse growing conditions, thus adding to the complexity of tRNA internal cleavage when confronting suboptimal growing conditions. However, in our experiments, elevated concentrations of oxygen as performed by Morrison et al. (38) could not induce the accumulation of sitRNAs (data not shown). It is reported that G. lamblia is a microaerophilic protozoan and can use different metabolic pathways under various concentrations of oxygen (19), so oxidative pressure is not stressful enough to induce tRNA cleavage. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Giardia lamblia is an early diverging and evolutionarily successful protozoan as it can enter into a dormant cyst stage from a vegetative trophozoite. During dormant stage, its metabolic rate decreases dramatically. However, to date, the regulatory molecules participating in the initiation and maintenance of this process have not been fully investigated. In this study, we have identified a class of abundant small RNAs named sitRNAs, which are ∼46 nucleotides in length and accumulate in G. lamblia encysting cultures. Remarkably, they are derived from the 3′ portion of fully matured tRNAs by cleavage of the anticodon left arm, with the 3′ terminal CCA triplex still connected. During differentiation, only a limited portion of mature tRNAs is cleaved, but this cleavage occurs almost in the entire tRNA family. sitRNAs begin to accumulate as early as 3 h after initiation of encystation and are maintained at a relatively stable level during the whole process, exhibiting an expression peak at around 24 hr. Our studies further show that sitRNAs can be induced by several other stress factors, and in the case of serum deprivation, both tRNAs and sitRNAs degrade rapidly, with the accumulation of tRNA being halved. Our results may provide new insight into a novel mechanism for stressed G. lamblia to regulate gene expression globally.
    Full-text · Article · Oct 2008 · Nucleic Acids Research
  • Source
    • "Secondly, the extant eukaryotic lineages diverged after the emergence of the major bacterial lineages, presumably even after the mitochondrial endosymbiosis (Hedges et al., 2001; Hedges, 2002), whereas the SahH sequences reflect the evolution of Proteobacteria . Moreover, the probable lack of SahH in the amitochondriate G. lamblia (though its primary amitochondriate status has been questioned recently, Morrison et al., 2001) might suggest that early diverging eukaryotes were missing this enzyme, which would rather support their bacterial origin. It is also known that some metabolic genes in eukaryotes group with bacteria and some of them lack phylogenetic affinity to the a-Proteobacteria or cyanobacteria, suggesting that they originate from other bacterial groups. "
    [Show abstract] [Hide abstract]
    ABSTRACT: S-Adenosylhomocysteine hydrolase (SahH) is involved in the degradation of the compound which inhibits methylation reactions. Using a Bayesian approach and other methods, we reconstructed a phylogenetic tree of amino acid sequences of this protein originating from all three major domains of living organisms. The SahH sequences formed two major branches: one composed mainly of Archaea and the other of eukaryotes and majority of bacteria, clearly contradicting the three-domain topology shown by small subunit rRNA gene. This topology suggests the occurrence of lateral transfer of this gene between the domains. Poor resolution of eukaryotes and bacteria excluded an ultimate conclusion in which out of the two domains this gene appeared first, however, the congruence of the secondary branches with SS rRNA and/or concatenated ribosomal protein datasets phylogenies suggested an “early” acquisition by some bacterial and eukaryotic phyla. Similarly, the branching pattern of Archaea reflected the phylogenies shown by SS rRNA and ribosomal proteins. SahH is widespread in Eucarya, albeit, due to reductive evolution, it is missing in the intracellular parasite Encephalitozoon cuniculi. On the other hand, the lack of affinity to the sequences from the α-Proteobacteria and cyanobacteria excludes a possibility of its acquisition in the course of mitochondrial or chloroplast endosymbioses.
    Full-text · Article · Feb 2005 · Molecular Phylogenetics and Evolution
  • Source
    • "Some, such as those of Entamoeba and Cryptosporidium, have been shown to contain chaperonin Cpn60, a protein known to participate in the refolding of imported proteins (Sigler et al., 1998; Mai et al., 1999; Tovar et al., 1999; Riordan et al., 2003); mitosomes of Trachipleistophora contain a mitochondrialtype Hsp70 (mtHsp70), a molecular motor that helps internalize proteins into the organelle (Matouschek et al., 2000; Williams et al., 2002). Other proteins have also been suggested as putative mitosomal components in various amitochondrial lineages but their cellular localization has not been demonstrated experimentally (Clark & Roger, 1995; Bakatselou et al., 2000, 2003; Katinka et al., 2001; Morrison et al., 2001; Zhu & Keithly, 2002; Arisue et al., 2002). Perhaps the most significant finding in relation to the biology of mitosomes is the direct demonstration that Giardia mitosomes function in the biosynthesis of molecular iron–sulphur (Fe–S) clusters and in their subsequent incorporation into functional Fe–S proteins (Tovar et al., 2003). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The existence of mitochondrion-related relict organelles (mitosomes) in the amitochondrial human pathogen Entamoeba histolytica and the detection of extranuclear DNA-containing cytoplasmic structures (EhKOs) has led to the suggestion that a remnant genome from the original mitochondrial endosymbiont might have been retained in this organism. This study reports on the mutually exclusive distribution of Cpn60 and extranuclear DNA in E. histolytica and on the distribution of Cpn60-containing mitosomes in this parasite. In situ nick-translation coupled to immunofluorescence microscopy failed to detect the presence of DNA in mitosomes, either in fixed parasite trophozoites or in partially purified organellar fractions. These results indicate that a remnant organellar genome has not been retained in E. histolytica mitosomes and demonstrate unequivocally that EhKOs and mitosomes are distinct and unrelated cellular structures.
    Full-text · Article · Jun 2004 · Microbiology
Show more