Ice-nucleating proteins (INPs) are among the most effective ice nucleators known. They are used by bacteria to induce frost damage to plants, and when airborne, they drive cloud formation and affect global precipitation patterns. Nevertheless, understanding how INPs order water into ice nuclei has remained an experimental and computational challenge, certainly in systems that approach the complexity of bacterial membranes. Previous studies in the field have focussed on INP mixtures from bacterial lysates, or proteins at the bare water surface. In this work, we investigate the molecular ordering imposed by a small purified INP from Pseudomonas syringae at lipid monolayers. The monolayers are chosen with increasing complexity, from a single composition lipid up to E.coli lipid extracts, thus building a model system, which approach the behaviour of INPs at real bacterial membrane interfaces. Using a combination of vibrational sum-frequency generation (vSFG) spectroscopy and molecular dynamics (MD) simulations, we show how the INP anchors itself to the lipid monolayer and reorients in response to a lowering temperature. In this way, the INP exposes its ice-active sites to the water molecules, which in turn become more ordered and, ultimately, better able to act as ice nuclei.

Ice-nucleating proteins at interfacial lipid monolayers

ACS Spring Meeting 2021

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