Engineering a naturally inactive isoform of type III antifreeze protein into one that can stop the growth of ice.

Type III antifreeze proteins (AFPs) can be sub-divided into three classes of isoforms. SP and QAE2 isoforms can slow, but not stop, the growth of ice crystals by binding to pyramidal ice planes. The other class (QAE1) binds both pyramidal and primary prism planes and is able to halt the growth of ice. Here we describe the conversion of a QAE2 isoform into a fully-active QAE1-like isoform by changing four surface-exposed residues to develop a primary prism plane binding site. Molecular dynamics analyses suggest that the basis for gain in antifreeze activity is the formation of ice-like waters on the mutated protein surface.