Structural Basis for the Superior Activity of the Large Isoform of Snow Flea Antifreeze Protein

Abstract

The snow flea (Hypogastrum harveyi) is protected from freezing at sub-zero temperatures by a glycine-rich antifreeze protein (AFP) that binds to seed ice crystals and prevents them, from growing larger. This AFP is hyperactive and comprises two isoforms [Graham, L. A., and Davies, P. L. (2005) Science 310, 461]. The larger isoform (15.7 kDa) exhibits several-fold higher activity than the smaller isoform (6.5 kDa), although it is considerably less abundant. To establish the molecular basis for this difference in activity, we determined the sequence of the large isoform. The primary sequences of these two isoforms are surprisingly divergent. However, both contain tripeptide repeats and turn mo..