Figure 8. A model for hAFP binding to [10-10] prism plane of ice.

(A) and (B) show that four ice-binding residues Asp94, Thr96, Thr98, and Glu99 form hydrogen bonds with water molecules of the ice lattice (highlighted in red) through respective side-chain oxygen atoms as indicated by yellow dotted lines. The Ca²⁺ ion is shown as a green sphere. The water molecule coordinating with the Ca²⁺ ion is shown as an orange sphere. The orientation of the ice lattice and the [10-10] prism plane are indicated. (C) Yellow spheres represent the water molecules constrained at the hAFP ice-binding face and the ice-water interface. (D) When hAFP binds to ice, constrained water molecules are released. This is considered as an entropy favorable process. (E) With the growth of the second layer of ice on the prism plane, the Ca²⁺-coordinating water molecule is incorporated into the ice lattice, thus the hAFP-ice interaction is further stabilized. This diagram was generated using PyMOL [41].