A new class of glutathione transferases has been discovered by analysis of the expressed sequence tag data base and sequence alignment. Glutathione S-transferases (GSTs) of the new class, named Omega, exist in several mammalian species and Caenorhabditis elegans. In humans, GSTO 1-1 is expressed in most tissues and exhibits glutathione-dependent thiol transferase and dehydroascorbate reductase activities characteristic of the glutaredoxins. The structure of GSTO 1-1 has been determined at 2.0-Å resolution and has a characteristic GST fold (Protein Data Bank entry code 1eem). The Omega class GSTs exhibit an unusual N-terminal extension that abuts the C terminus to form a novel structural unit. Unlike other mammalian GSTs, GSTO 1-1 appears to have an active site cysteine that can form a disulfide bond with glutathione.

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Background Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests.ResultsWe find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes.ConclusionsThe extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera’s invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-017-0402-6) contains supplementary material, which is available to authorized users.

Expression of recombinant proteins as fusions to the eukaryotic protein ubiquitin has been found to significantly increase the yield of unstable or poorly expressed proteins. The benefit of this technique is further enhanced by the availability of naturally occurring deubiquitylating enzymes, which remove ubiquitin from the fusion product. However, the versatility of the system has been constrained due to the lack of a robust, easily purified deubiquitylating enzyme. Here we report the development of an efficient expression system, utilizing the ubiquitin fusion technique, which allows convenient high yield and easy purification of authentic protein. An Escherichia coli vector (pHUE) was constructed for the expression of proteins as histidine-tagged ubiquitin fusions, and a histidine-tagged deubiquitylating enzyme to cleave these fusions was expressed and purified. The expression system was tested using several proteins varying in size and complexity. These results indicate that this procedure will be suitable for the expression and rapid purification of a broad range of proteins and peptides, and should be amenable to high-throughput applications.

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The major differences among the three structures reported here involve the C-terminal alpha-helix, which is a characteristic of the alpha-class enzyme. This helix forms a lid over the active site when the hydrophobic substrate binding site (H-site) is occupied but it is otherwise disordered. Ethacrynic acid appears to bind in a non-productive mode in the absence of the coenzyme glutathione.

Glutathione S‐transferases (GSTs) are a family of enzymes involved in the cellular detoxification of xenotoxins. Cytosolic GSTs have been grouped into four evolutionary classes for which there are representative crystal structures of three of them. Here we report the first crystal structure of a theta‐class GST. So far, all available GST crystal structures suggest that a strictly conserved tyrosine near the N‐terminus plays a critical role in the reaction mechanism and such a role has been convincingly demonstrated by site‐directed mutagenesis. Surprisingly, the equivalent residue in the theta‐class structure is not in the active site, but its role appears to have been replaced by either a nearby serine or by another tyrosine residue located in the C‐terminal domain of the enzyme.