Three amino acid substitutions contributing to thermostability of phosphoglucose isomerase in the Glanville fritillary butterfly

Temperature is one of the most important environmental factors that affect organisms,especially ectotherms,due to its effects on protein stability.Understanding the general rules that govern thermostability changes in proteins to adapt high-temperature environments is crucial.Here,we report the amino acid substitutions of phosphoglucose isomerase(PGI)related to thermostability in the Glanville fritillary butterfly(Melitaea cinxia,Lepidoptera:Nymphalidae).The PGI encoded by the most common allele in M.cinxia in the Chinese population(G3-PGI),which is more thermal tolerant,is more stable under heat stress than that in the Finnish population(D1-PGI).There are 5 amino acid substitutions between G3-PGI and D1-PGI.Site-directed mutagenesis revealed that the combination of amino acid substitutions of H35Q,M49T,and I64V may increase PGI thermostability.These substitutions alter the 3D structure to increase the interaction between 2 monomers of PGI.Through molecular dynamics simulations,it was found that the amino acid at site 421 is more stable in G3-PGI,confining the motion of theα-helix 420-441 and stabilizing the interaction between 2 PGI monomers.The strategy for hightemperature adaptation through these 3 amino acid substitutions is also adopted by other butterfly species(Boloria eunomia,Aglais urticae,Colias erate,and Polycaena lua)concurrent with M.cinxia in the Tianshan Mountains of China,i.e.,convergent evolution in butterflies.

Drosophila, destroying angels, and deathcaps! Oh my! A review of mycotoxin tolerance in the genus Drosophila

BACKGROUND： Evolutionary novelties, be they morphological or biochemical, fascinate both scientists and non-scientists alike. These types of adaptations can significantly impact the biodiversity of the organisms in which they occur. While much work has been invested in the evolution of novel morphological traits, substantially less is known about the evolution of biochemical adaptations. METHODS： In this review, we present the results of literature searches relating to one such biochemical adaptation： α- amanitin tolerance/resistance in the genus Drosophila. RESULTS： Amatoxins, including α-amanitin, are one of several toxin classes found in Amanita mushrooms. They act by binding to RNA polymerase Ⅱ and inhibiting RNA transcription. Although these toxins are lethal to most eukaryotic organisms, 17 mushroom-feeding Drosophila species are tolerant of natural concentrations of amatoxins and can develop in toxic mushrooms. The use of toxic mushrooms allows these species to avoid infection by parasitic nematodes and lowers competition. Their amatoxin tolerance is not due to mutations that would inhibit α-amanitin from binding to RNA polymerase Ⅱ. Furthermore, the mushroom-feeding flies are able to detoxify the other toxin classes that occur in their mushroom hosts. In addition, resistance has evolved independently in several D. melanogaster strains. Only one of the strains exhibits resistance due to mutations in the target of the toxin. CONCLUSIONS： Given our current understanding of the evolutionary relationships among the mushroom-feeding flies, it appears that amatoxin tolerance evolved multiple times. Furthermore, independent lines of evidence suggest that multiple mechanisms confer α-amanitin tolerance/resistance in Drosophila.