Freezing and Melting Hysteresis Measurements in Solutions of Hyperactive Antifreeze Protein from an Antarctic Bacteria

TL;DR

This study demonstrates that a hyperactive antifreeze protein from Antarctic bacteria can inhibit both freezing and melting of ice, showing superheating and reversible overgrowth, indicating irreversible binding to ice surfaces.

Contribution

It provides the first quantitative evidence of melting inhibition by hyperactive AFPs and reveals their ability to reversibly overgrow and melt ice crystals.

Findings

Hyperactive AFP inhibits ice melting, causing superheating.

Ice crystals can be overgrown and then melted back to original form.

AFP binding to ice is likely irreversible.

Abstract

Antifreeze proteins (AFPs) evolved in cold-adapted organisms and serve to protect them against freezing in cold conditions by arresting ice crystal growth. Recently, we have shown quantitatively that adsorption of AFPs not only prevents ice from growing but also from melting. This melting inhibition by AFPs, which results in superheated ice (Celik et al, PNAS 2010), is not a well-known phenomenon. Here we present our recent findings in which the Ca2+ - dependent hyperactive AFP from Marinomonas primoryensis (MpAFP) clearly displays this property. Additionally, we found that an ice crystal that is initially stabilized and protected by this type of AFP can be overgrown and then melted back to the original crystal. This repeatable process is likely due to melting inhibition, and supports the idea that AFPs bind irreversibly to ice surfaces.