Fully Atomistic Molecular Dynamics Simulation of Ice Nucleation Near an Antifreeze Protein.

Heterogeneous ice nucleation is a widespread phenomenon in nature. Despite extensive research on ice nucleation near biological antifreeze proteins, a probe for ice nucleation and growth processes at the atomic level is still lacking. Herein, we present simulation evidence of the heterogeneous ice nucleation process on the ice-binding surface (IBS) of the antifreeze protein (TmAFP). Our all-atomistic molecular dynamics simulations reveal detailed steps toward precritical nucleus formation from one-dimensional (1D) channel water to a 2D ice nanolayer and, finally, a 3D ice nucleus. Compared with homogeneous ice nucleation under the same supercooling conditions, the IBS of TmAFP can markedly reduce the critical size of the ice embryo and lower the nucleation free energy barrier, thereby favoring ice nucleation. Additionally, through artificial mutation of selected functional groups on the IBS, we gain deeper insights into how the specific functional groups of the IBS affect ice nucleation. We highlight that the carbonyl groups in the backbone play a crucial role by providing fixed locations for channel water. This function is essential for ensuring alignment between the 2D ice nanolayer and the ice lattice structure.