Exploring three different expression systems for recombinant expression of globins: Escherichia coli, Pichia pastoris and Spodoptera frugiperda

Globins are among the best investigated proteins in biological and medical sciences and represent a prime tool for the study of the evolution of genes and the structure- function relationship of proteins. Here, we explore the recombinant expression of globins in three different expression systems: Escherichia coli, Pichia pastoris and the baculovirus infected Spodoptera frugiperda. We expressed two different human globin types in these three expression systems: I) the well-characterized neuroglobin and II) the uncharacterized, circular permutated globin domain of the large chimeric globin androglobin. It is clear from the literature that E.coli is the most used expression system for expression and purification of recombinant globins. However, the major disadvantage of E. coli is the formation of insoluble aggregates. We experienced that, for more complex multi-domain globins, like the chimeric globin androglobin, it is recommended to switch to a higher eukaryotic expression system

The Putative RNA Helicase HELZ Promotes Cell Proliferation, Translation Initiation and Ribosomal Protein S6 Phosphorylation

The hypoxia–inducible transcription factor (HIF) is a key component of the cellular adaptation mechanisms to hypoxic conditions. HIFα subunits are degraded by prolyl-4-hydroxylase domain (PHD) enzyme-dependent prolyl-4-hydroxylation of LxxLAP motifs that confer oxygen-dependent proteolytic degradation. Interestingly, only three non-HIFα proteins contain two conserved LxxLAP motifs, including the putative RNA helicase with a zinc finger domain HELZ. However, HELZ proteolytic regulation was found to be oxygen-independent, supporting the notion that a LxxLAP sequence motif alone is not sufficient for oxygen-dependent protein destruction. Since biochemical pathways involving RNA often require RNA helicases to modulate RNA structure and activity, we used luciferase reporter gene constructs and metabolic labeling to demonstrate that HELZ overexpression activates global protein translation whereas RNA-interference mediated HELZ suppression had the opposite effect. Although HELZ interacted with the poly(A)-binding protein (PABP) via its PAM2 motif, PABP was dispensable for HELZ function in protein translation. Importantly, downregulation of HELZ reduced translational initiation, resulting in the disassembly of polysomes, in a reduction of cell proliferation and hypophosphorylation of ribosomal protein S6

Wide diversity in structure and expression profiles among members of the Caenorhabditis elegans globin protein family

<p>Abstract</p> <p>Background</p> <p>The emergence of high throughput genome sequencing facilities and powerful high performance bioinformatic tools has highlighted hitherto unexpected wide occurrence of globins in the three kingdoms of life. <it>In silico </it>analysis of the genome of <it>C. elegans </it>identified 33 putative globin genes. It remains a mystery why this tiny animal might need so many globins. As an inroad to understanding this complexity we initiated a structural and functional analysis of the globin family in <it>C. elegans</it>.</p> <p>Results</p> <p>All 33 <it>C. elegans </it>putative globin genes are transcribed. The translated sequences have the essential signatures of single domain <it>bona fide </it>globins, or they contain a distinct globin domain that is part of a larger protein. All globin domains can be aligned so as to fit the globin fold, but internal interhelical and N- and C-terminal extensions and a variety of amino acid substitutions generate much structural diversity among the globins of <it>C. elegans</it>. Likewise, the encoding genes lack a conserved pattern of intron insertion positioning. We analyze the expression profiles of the globins during the progression of the life cycle, and we find that distinct subsets of globins are induced, or repressed, in wild-type dauers and in <it>daf-2(e1370)</it>/insulin-receptor mutant adults, although these animals share several physiological features including resistance to elevated temperature, oxidative stress and hypoxic death. Several globin genes are upregulated following oxygen deprivation and we find that HIF-1 and DAF-2 each are required for this response. Our data indicate that the DAF-2 regulated transcription factor DAF-16/FOXO positively modulates <it>hif-1 </it>transcription under anoxia but opposes expression of the HIF-1 responsive globin genes itself. In contrast, the canonical globin of <it>C. elegans</it>, ZK637.13, is not responsive to anoxia. Reduced DAF-2 signaling leads to enhanced transcription of this globin and DAF-16 is required for this effect.</p> <p>Conclusion</p> <p>We found that all 33 putative globins are expressed, albeit at low or very low levels, perhaps indicating cell-specific expression. They show wide diversity in gene structure and amino acid sequence, suggesting a long evolutionary history. Ten globins are responsive to oxygen deprivation in an interacting HIF-1 and DAF-16 dependent manner. Globin ZK637.13 is not responsive to oxygen deprivation and regulated by the Ins/IGF pathway only suggesting that this globin may contribute to the life maintenance program.</p

Frequently asked questions in hypoxia research

“What is the O2 concentration in a normoxic cell culture incubator?” This and other frequently asked questions in hypoxia research will be answered in this review. Our intention is to give a simple introduction to the physics of gases that would be helpful for newcomers to the field of hypoxia research. We will provide background knowledge about questions often asked, but without straightforward answers. What is O2 concentration, and what is O2 partial pressure? What is normoxia, and what is hypoxia? How much O2 is experienced by a cell residing in a culture dish in vitro vs in a tissue in vivo? By the way, the O2 concentration in a normoxic incubator is 18.6%, rather than 20.9% or 20%, as commonly stated in research publications. And this is strictly only valid for incubators at sea level

A phylogenomic profile of globins

BACKGROUND: Globins occur in all three kingdoms of life: they can be classified into single-domain globins and chimeric globins. The latter comprise the flavohemoglobins with a C-terminal FAD-binding domain and the gene-regulating globin coupled sensors, with variable C-terminal domains. The single-domain globins encompass sequences related to chimeric globins and «truncated» hemoglobins with a 2-over-2 instead of the canonical 3-over-3 α-helical fold. RESULTS: A census of globins in 26 archaeal, 245 bacterial and 49 eukaryote genomes was carried out. Only ~25% of archaea have globins, including globin coupled sensors, related single domain globins and 2-over-2 globins. From one to seven globins per genome were found in ~65% of the bacterial genomes: the presence and number of globins are positively correlated with genome size. Globins appear to be mostly absent in Bacteroidetes/Chlorobi, Chlamydia, Lactobacillales, Mollicutes, Rickettsiales, Pastorellales and Spirochaetes. Single domain globins occur in metazoans and flavohemoglobins are found in fungi, diplomonads and mycetozoans. Although red algae have single domain globins, including 2-over-2 globins, the green algae and ciliates have only 2-over-2 globins. Plants have symbiotic and nonsymbiotic single domain hemoglobins and 2-over-2 hemoglobins. Over 90% of eukaryotes have globins: the nematode Caenorhabditis has the most putative globins, ~33. No globins occur in the parasitic, unicellular eukaryotes such as Encephalitozoon, Entamoeba, Plasmodium and Trypanosoma. CONCLUSION: Although Bacteria have all three types of globins, Archaeado not have flavohemoglobins and Eukaryotes lack globin coupled sensors. Since the hemoglobins in organisms other than animals are enzymes or sensors, it is likely that the evolution of an oxygen transport function accompanied the emergence of multicellular animals

The Caenorhabditis globin gene family reveals extensive nematode-specific radiation and diversification

<p>Abstract</p> <p>Background</p> <p>Globin isoforms with variant properties and functions have been found in the pseudocoel, body wall and cuticle of various nematode species and even in the eyespots of the insect-parasite <it>Mermis nigrescens</it>. In fact, much higher levels of complexity exist, as shown by recent whole genome analysis studies. <it>In silico </it>analysis of the genome of <it>Caenorhabditis elegans </it>revealed an unexpectedly high number of globin genes featuring a remarkable diversity in gene structure, amino acid sequence and expression profiles.</p> <p>Results</p> <p>In the present study we have analyzed whole genomic data from <it>C. briggsae</it>, <it>C. remanei</it>, <it>Pristionchus pacificus </it>and <it>Brugia malayi </it>and EST data from several other nematode species to study the evolutionary history of the nematode globin gene family. We find a high level of conservation of the <it>C. elegans </it>globin complement, with even distantly related nematodes harboring orthologs to many <it>Caenorhabditis </it>globins. Bayesian phylogenetic analysis resolves all nematode globins into two distinct globin classes. Analysis of the globin intron-exon structures suggests extensive loss of ancestral introns and gain of new positions in deep nematode ancestors, and mainly loss in the <it>Caenorhabditis </it>lineage. We also show that the <it>Caenorhabditis </it>globin genes are expressed in distinct, mostly non-overlapping, sets of cells and that they are all under strong purifying selection.</p> <p>Conclusion</p> <p>Our results enable reconstruction of the evolutionary history of the globin gene family in the nematode phylum. A duplication of an ancestral globin gene occurred before the divergence of the Platyhelminthes and the Nematoda and one of the duplicated genes radiated further in the nematode phylum before the split of the Spirurina and Rhabditina and was followed by further radiation in the lineage leading to <it>Caenorhabditis</it>. The resulting globin genes were subject to processes of subfunctionalization and diversification leading to cell-specific expression patterns. Strong purifying selection subsequently dampened further evolution and facilitated fixation of the duplicated genes in the genome.</p

Transcriptome-based network analysis reveals renal cell type-specific dysregulation of hypoxia-associated transcripts

Accumulating evidence suggests that dysregulation of hypoxia-regulated transcriptional mechanisms is involved in development of chronic kidney diseases (CKD). However, it remains unclear how hypoxia-induced transcription factors (HIFs) and subsequent biological processes contribute to CKD development and progression. In our study, genome-wide expression profiles of more than 200 renal biopsies from patients with different CKD stages revealed significant correlation of HIF-target genes with eGFR in glomeruli and tubulointerstitium. These correlations were positive and negative and in part compartment-specific. Microarrays of proximal tubular cells and podocytes with stable HIF1α and/or HIF2α suppression displayed cell type-specific HIF1/HIF2-dependencies as well as dysregulation of several pathways. WGCNA analysis identified gene sets that were highly coregulated within modules. Characterization of the modules revealed common as well as cell group- and condition-specific pathways, GO-Terms and transcription factors. Gene expression analysis of the hypoxia-interconnected pathways in patients with different CKD stages revealed an increased dysregulation with loss of renal function. In conclusion, our data clearly point to a compartment- and cell type-specific dysregulation of hypoxia-associated gene transcripts and might help to improve the understanding of hypoxia, HIF dysregulation, and transcriptional program response in CKD

Globin-like proteins in Caenorhabditis elegans: in vivo localization, ligand binding and structural properties

Background: The genome of the nematode Caenorhabditis elegans contains more than 30 putative globin genes that all are transcribed. Although their translated amino acid sequences fit the globin fold, a variety of amino-acid substitutions and extensions generate a wide structural diversity among the putative globins. No information is available on the physicochemical properties and the in vivo expression. Results: We expressed the globins in a bacterial system, characterized the purified proteins by optical and resonance Raman spectroscopy, measured the kinetics and equilibria of O2 binding and determined the crystal structure of GLB-1* (CysGH2 T Ser mutant). Furthermore, we studied the expression patterns of glb-1 (ZK637.13) and glb-26 (T22C1.2) in the worms using green fluorescent protein technology and measured alterations of their transcript abundances under hypoxic conditions.GLB-1* displays the classical three-over-three α-helical sandwich of vertebrate globins, assembled in a homodimer associated through facing E- and F-helices. Within the heme pocket the dioxygen molecule is stabilized by a hydrogen bonded network including TyrB10 and GlnE7.GLB-1 exhibits high ligand affinity, which is, however, lower than in other globins with the same distal TyrB10-GlnE7 amino-acid pair. In the absence of external ligands, the heme ferrous iron of GLB-26 is strongly hexacoordinated with HisE7, which could explain its extremely low affinity for CO. This globin oxidizes instantly to the ferric form in the presence of oxygen and is therefore incapable of reversible oxygen binding. Conclusion: The presented data indicate that GLB-1 and GLB-26 belong to two functionally-different globin classes

Electron Transfer Function versus Oxygen Delivery: A Comparative Study for Several Hexacoordinated Globins Across the Animal Kingdom

Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O2 and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O2 as for Ngb and Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O2 actually binding to the iron atom, since the heme is oxidized by O2 faster than the time for distal histidine dissociation. These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally different from that of pentacoordinated globins

Phylogeny of Echinoderm Hemoglobins

Recent genomic information has revealed that neuroglobin and cytoglobin are the two principal lineages of vertebrate hemoglobins, with the latter encompassing the familiar myoglobin and α-globin/β-globin tetramer hemoglobin, and several minor groups. In contrast, very little is known about hemoglobins in echinoderms, a phylum of exclusively marine organisms closely related to vertebrates, beyond the presence of coelomic hemoglobins in sea cucumbers and brittle stars. We identified about 50 hemoglobins in sea urchin, starfish and sea cucumber genomes and transcriptomes, and used Bayesian inference to carry out a molecular phylogenetic analysis of their relationship to vertebrate sequences, specifically, to assess the hypothesis that the neuroglobin and cytoglobin lineages are also present in echinoderms.The genome of the sea urchin Strongylocentrotus purpuratus encodes several hemoglobins, including a unique chimeric 14-domain globin, 2 androglobin isoforms and a unique single androglobin domain protein. Other strongylocentrotid genomes appear to have similar repertoires of globin genes. We carried out molecular phylogenetic analyses of 52 hemoglobins identified in sea urchin, brittle star and sea cucumber genomes and transcriptomes, using different multiple sequence alignment methods coupled with Bayesian and maximum likelihood approaches. The results demonstrate that there are two major globin lineages in echinoderms, which are related to the vertebrate neuroglobin and cytoglobin lineages. Furthermore, the brittle star and sea cucumber coelomic hemoglobins appear to have evolved independently from the cytoglobin lineage, similar to the evolution of erythroid oxygen binding globins in cyclostomes and vertebrates.The presence of echinoderm globins related to the vertebrate neuroglobin and cytoglobin lineages suggests that the split between neuroglobins and cytoglobins occurred in the deuterostome ancestor shared by echinoderms and vertebrates