LAUSR

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 five 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 two 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 the α-helix 420-441 and stabilizing the interaction between two PGI monomers. The strategy for high-temperature adaptation through these three 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. This article is protected by copyright. All rights reserved.