Adsorption Barrier Limits the Ice Inhibition Activity of Glycan-Rich Antifreeze Glycoproteins

Antifreeze glycoproteins (AFGPs) are among the most potent ice recrystallization inhibition (IRI) agents, yet the molecular basis for their counterintuitive decline in activity with increasing glycosylated threonine (T*) content remains unresolved. Through molecular dynamics simulations of model glycoproteins with increasing T* content, we show that the potent IRI activity of AFGPs arises not only from the thermodynamic stability of strong ice-binding states but also from their kinetic accessibility. Specifically, the free energy barrier for forming strong ice-binding states from the unbound state constitutes a critical kinetic bottleneck. Increasing the T* content enhances the overall hydration capacity due to the additional glycan moieties, thereby imposing a greater desolvation penalty and elevating the adsorption barrier. This kinetic limitation, rather than the absence of strong ice-binding states, accounts for the observed decline in the IRI activity. To quantify the structural basis of this behavior, we introduce a facial amphiphilicity index that integrates both spatial segregation and compositional ratio of hydrophilic and hydrophobic residues and show that it correlates well with IRI activity. These findings highlight that facial amphiphilicity mediates a critical balance between binding stability and kinetic accessibility, providing a rational design principle for advanced IRI materials.