On the Engulfment of Antifreeze Proteins by Ice
Antifreeze proteins (AFPs) are remarkable biomolecules that suppress ice formation at trace concentrations. To inhibit ice growth, AFPs must not only bind to ice crystals, but also resist engulfment by ice. The highest supercooling, $\Delta T^{*}$, for which AFPs are able to resist engulfment is widely believed to scale as the inverse of the separation, $L$, between bound AFPs, whereas its dependence on the molecular characteristics of the AFP remains poorly understood. By using specialized molecular simulations and interfacial thermodynamics, here we show that in contrast with conventional wisdom, $\Delta T^{*}$ scales as $L^{-2}$ and not as $L^{-1}$. We further show that $\Delta T^{*}$ is proportional to AFP size and that diverse naturally occurring AFPs are optimal at resisting engulfment by ice. By facilitating the development of AFP structure-function relationships, we hope that our findings will pave the way for the rational design of novel AFPs.