Cooperative\nRole of Conformation and Ice-Binding Groups\nin Ice Growth Inhibition of Antifreeze Glycoproteins

The antifreeze mechanism of antifreeze glycoproteins\n(AFGPs) remains\nincompletely understood, which limits the design of new antifreeze\nmolecules for practical applications. For instance, the ice growth\ninhibition of AFGP8 (the shortest AFGPs) is primarily driven by hydrophobic\nmethyl and hydrogen-bonding hydroxyl groups. However, altering the\nC3-β linkage in the disaccharide moiety of AFGP8, denoted as\nvariant GP8-LacNAc, significantly reduces its antifreeze activity.\nThis challenges the conventional understanding of the antifreeze activity\nof AFGP8 because no group is removed. Here, we revisit the antifreeze\nmechanism using molecular dynamics simulations of two AFGPs as an\nexample, revealing the relation between conformation, ice-binding\ngroup, and ice growth inhibition activity. The PPII helix is not the\nreason for the weak activity of GP8-LacNAc, while the cooperativity\nof the conformation and group matters. AFGP8 maintains a dominant\nconformation with all four disaccharides on the same side, which maximizes\nthe binding with ice. While GP8-LacNAc undergoes frequent conformational\ntransitions, leading to a methyl-hydroxyl distance mismatch with the\nice surface. Our results reveal the cooperative role of conformation\nand ice-binding groups, providing new insights into the antifreeze\nmechanism of flexible proteins.