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Effects of mRNA secondary structure on the expression of HEV ORF2 proteins in Escherichia coli.

ABSTRACT: Viral protein expression in Escherichia coli (E. coli) is a powerful tool for structural/functional studies as well as for vaccine and diagnostics development. However, numerous factors such as codon bias, mRNA secondary structure and nucleotides distribution, have been indentified to hamper this heterologous expression.In this study, we combined computational and biochemical methods to analyze the influence of these factors on the expression of different segments of hepatitis E virus (HEV) ORF 2 protein and hepatitis B virus surface antigen (HBsAg). Three out of five HEV antigens were expressed while all three HBsAg fragments were not. The computational analysis revealed a significant difference in nucleotide distribution between expressed and non-expressed genes; and all these non-expressing constructs shared similar stable 5'-end mRNA secondary structures that affected the accessibility of both Shine-Dalgarno (SD) sequence and start codon AUG. By modifying the 5'-end of HEV and HBV non-expressed genes, there was a significant increase in the total free energy of the mRNA secondary structures that permitted the exposure of the SD sequence and the start codon, which in turn, led to the successful expression of these genes in E. coli.This study demonstrates that the mRNA secondary structure near the start codon is the key limiting factor for an efficient expression of HEV ORF2 proteins in E. coli. It describes also a simple and effective strategy for the production of viral proteins of different lengths for immunogenicity/antigenicity comparative studies during vaccine and diagnostics development.

SUBMITTER: Behloul N

PROVIDER: S-EPMC5686824 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Effects of mRNA secondary structure on the expression of HEV ORF2 proteins in Escherichia coli.

Behloul Nouredine N Wei Wenjuan W Baha Sarra S Liu Zhenzhen Z Wen Jiyue J Meng Jihong J

Microbial cell factories 20171114 1

<h4>Background</h4>Viral protein expression in Escherichia coli (E. coli) is a powerful tool for structural/functional studies as well as for vaccine and diagnostics development. However, numerous factors such as codon bias, mRNA secondary structure and nucleotides distribution, have been indentified to hamper this heterologous expression.<h4>Results</h4>In this study, we combined computational and biochemical methods to analyze the influence of these factors on the expression of different segme ...[more]

PMID: 29137642

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Project description:BACKGROUND:Hepatitis E virus (HEV) is a causative agent of acute hepatitis among people of different age groups and has high mortality rate of up to 30% among pregnant women. Therefore, primary prevention of HEV infection is essential. OBJECTIVES:The aim of this study was to obtain the highly purified truncated open reading frames 2 (ORF2) protein, which might be a future HEV vaccine candidate. MATERIALS AND METHODS:The truncated orf2 gene (orf2.1), encoding the 112-660 amino acid of HEV capsid protein sequence, was optimized, synthesized, and cloned into pBluescript II SK(+) vector. After subcloning into expression vector pET-30a (+), a 193-nucleotide fragment was deleted from the construct and the recombinant plasmid pET-30a-ORF2.2 (orf2.2 encodes 112-608 amino acid sequence of HEV capsid protein) was constructed and used for transformation of Escherichia coli BL21 cells. After induction with isopropyl-?-D-thiogalactopyranoside (IPTG) and optimizing the conditions of expression, the target protein was highly expressed and purified by Ni(2+)-chelate affinity chromatography. The expressed and purified protein was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. RESULTS:The subcloning was confirmed by PCR, restriction enzyme digestion, and DNA sequencing of recombinant plasmid pET30a-ORF2.2. The results obtained from optimizing the expression conditions showed that the highest expression of the protein was obtained by adding IPTG at a final concentration of 1 mM at 37? for four hours. The expression and purification of truncated ORF2 protein was confirmed by SDS-PAGE and western blotting. SDS-PAGE analysis showed a protein band of about 55 kDa. SDS-PAGE of the purified protein revealed that the highest amount of target protein in elution buffer at the pH of 4.5 was obtained. The yield of the purified protein was about 1 mg/L of culture media. CONCLUSIONS:In this study, the optimized truncated ORF2 protein was expressed in E. coli successfully and the highly purified protein was obtained, which can be a potential vaccine candidate and as an antigen in ELISA to diagnose HEV infections.

Project description:BackgroundEscherichia coli exhibits diauxic growth in sugar mixtures due to CRP-mediated catabolite repression and inducer exclusion related to phosphotransferase system enzyme activity. Replacement of the native crp gene with a catabolite repression mutant (referred to as crp*) enables co-utilization of glucose and other sugars in E. coli. While previous studies have examined the effects of expressing CRP* mutants on the expression of specific catabolic genes, little is known about the global transcriptional effects of CRP* expression. In this study, we compare the transcriptome of E. coli W3110 (expressing wild-type CRP) to that of mutant strain PC05 (expressing CRP*) in the presence and absence of glucose.ResultsThe glucose effect is significantly suppressed in strain PC05 relative to strain W3110. The expression levels of glucose-sensitive genes are generally not altered by glucose to the same extent in strain PCO5 as compared to W3110. Only 23 of the 80 genes showing significant differential expression in the presence of glucose for strain PC05 are present among the 418 genes believed to be directly regulated by CRP. Genes involved in central carbon metabolism (including several TCA cycle genes) and amino acid biosynthesis, as well as genes encoding nutrient transport systems are among those whose transcript levels are most significantly affected by CRP* expression.We present a detailed transcription analysis and relate these results to phenotypic differences between strains expressing wild-type CRP and CRP*. Notably, CRP* expression in the presence of glucose results in an elevated intracellular NADPH concentration and reduced NADH concentration relative to wild-type CRP. Meanwhile, a more drastic decrease in the NADPH/NADP+ ratio is observed for the case of CRP* expression in strains engineered to reduce xylose to xylitol via a heterologously expressed, NADPH-dependent xylose reductase. Altered expression levels of transhydrogenase and TCA cycle genes, among others, are consistent with these observations.ConclusionWhile the simplest model of CRP*-mediated gene expression assumes insensitivity to glucose (or cAMP), our results show that gene expression in the context of CRP* is very different from that of wild-type in the absence of glucose, and is influenced by the presence of glucose. Most of the transcription changes in response to CRP* expression are difficult to interpret in terms of possible systematic effects on metabolism. Elevated NADPH availability resulting from CRP* expression suggests potential biocatalytic applications of crp* strains that extend beyond relief of catabolite repression.

Project description:Avian hepatitis E virus (HEV) is the main causative agent of big liver and spleen disease in chickens. Due to the absence of a highly effective cell culture system, there are few reports about the interaction between avian HEV and host cells. In this study, organic anion-transporting polypeptide 1A2 (OATP1A2) from chicken liver cells was identified to interact with ap237, a truncated avian HEV capsid protein spanning amino acids 313 to 549, by a glutathione S-transferase (GST) pulldown assay. GST pulldown and indirect enzyme-linked immunosorbent assays (ELISAs) further confirmed that the extracellular domain of OATP1A2 directly binds with ap237. The expression levels of OATP1A2 in host cells are positively correlated with the amounts of ap237 attachment and virus infection. The distribution of OATP1A2 in different tissues is consistent with avian HEV infection in vivo Finally, when the functions of OATP1A2 in cells are inhibited by its substrates or an inhibitor or blocked by ap237 or anti-OATP1A2 sera, attachment to and infection of host cells by avian HEV are significantly reduced. Collectively, these results displayed for the first time that OATP1A2 interacts with the avian HEV capsid protein and can influence viral infection in host cells. The present study provides new insight to understand the process of avian HEV infection of host cells.IMPORTANCE The process of viral infection is centered around the interaction between the virus and host cells. Due to the lack of a highly effective cell culture system in vitro, there is little understanding about the interaction between avian HEV and its host cells. In this study, a total of seven host proteins were screened in chicken liver cells by a truncated avian HEV capsid protein (ap237) in which the host protein OATP1A2 interacted with ap237. Overexpression of OATP1A2 in the cells can promote ap237 adsorption as well as avian HEV adsorption and infection of the cells. When the function of OATP1A2 in cells was inhibited by substrates or inhibitors, attachment and infection by avian HEV significantly decreased. The distribution of OATP1A2 in different chicken tissues corresponded with that in tissues during avian HEV infection. This is the first finding that OATP1A2 is involved in viral infection of host cells.

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Effects of mRNA secondary structure on the expression of HEV ORF2 proteins in Escherichia coli.

Publications

Effects of mRNA secondary structure on the expression of HEV ORF2 proteins in Escherichia coli.

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