Discovery of Hyperactive Antifreeze Protein from Phylogenetically Distant Beetles Questions Its Evolutionary Origin

Beetle hyperactive antifreeze protein (AFP) has a unique ability to maintain a supercooling state of its body fluids, however, less is known about its origination. Here, we found that a popular stag beetle Dorcus hopei binodulosus (Dhb) synthesizes at least 6 isoforms of hyperactive AFP (DhbAFP). Cold-acclimated Dhb larvae tolerated -5 degrees C chilled storage for 24 h and fully recovered after warming, suggesting that DhbAFP facilitates overwintering of this beetle. A DhbAFP isoform (similar to 10 kDa) appeared to consist of 6-8 tandem repeats of a 12-residue consensus sequence (TCTxSxNCxxAx), which exhibited 3 degrees C of high freezing point depression and the ability of binding to an entire surface of a single ice crystal. Significantly, these properties as well as DNA sequences including the untranslated region, signal peptide region, and an AFP-encoding region of Dhb are highly similar to those identified for a known hyperactive AFP (TmAFP) from the beetle Tenebrio molitor (Tm). Progenitor of Dhb and Tm was branched off approximately 300 million years ago, so no known evolution mechanism hardly explains the retainment of the DNA sequence for such a long divergence period. Existence of unrevealed gene transfer mechanism will be hypothesized between these two phylogenetically distant beetles to acquire this type of hyperactive AFP.

Automated summary

The study found that the popular stag beetle synthesizes multiple isoforms of hyperactive antifreeze protein, which helps the beetle survive extreme freezing conditions. The DNA sequences of the beetle are highly similar to those of other hyperactive antifreeze proteins, suggesting a potential unrevealed gene transfer mechanism.