Engineering Antifreeze Proteins to Optimally Resist Engulfment by Ice

Area of Science:

• Biophysics
• Materials Science
• Cryobiology

Background:

• Antifreeze proteins (AFPs) are vital for organisms surviving in cold environments.
• AFPs inhibit ice crystal growth and recrystallization by binding to ice surfaces.
• Effective AFP function requires resisting engulfment by ice via the nonbinding side (NBS).

Purpose of the Study:

• To investigate how molecular characteristics of the NBS, like ice-phobicity and shape, affect AFP resistance to ice engulfment.
• To determine the relationship between NBS properties and the critical supercooling temperature (ΔT*) at which AFPs are engulfed.

Main Methods:

• Characterization of free energy barriers impeding model AFP engulfment.
• Analysis of the interplay between contact line perimeter (P) and pinning efficiency (η) on the NBS.
• Modeling of different NBS shapes, including hemispherical, outward-tapering, and a proposed outward-bulge design.

Main Results:

• Critical supercooling (ΔT*) is dictated by an optimal pinning site on the NBS, determined by the product of pinning efficiency (η) and contact line perimeter (P) (ΔT* ∝ ηP).
• A hemispherical NBS shows limited ΔT* due to an inverse correlation between increasing η and decreasing P during engulfment.
• An outward-bulge NBS design significantly enhances ΔT* (over twofold increase with a 1 nm bulge) by optimizing both P and η.
• Increased NBS ice-phobicity directly improves pinning efficiency and elevates ΔT*.

Conclusions:

• NBS molecular characteristics, particularly shape and ice-phobicity, critically influence AFP's ability to resist ice engulfment.
• An outward-bulge NBS design represents a promising strategy for engineering enhanced ice-resistance in AFPs.
• Findings provide insights for designing novel AFPs with superior cryoprotective properties.