Role of glycopeptides and pepddes in inhibition of crystallization of water in polar fishes

Abstract

In the ice-laden polar oceans, water temperatures of — 2 °C are common. This temperature is 1.1 °C below the equilibrium freezing point ( — 0.9 °C) of the fishes’ body fluids. Avoidance of freezing in these environments has been linked to the presence of unusual blood peptides and glycopeptides. These molecules have molecular masses ranging from 2.5 to 20 kDa and are viewed as having antifreeze properties because they lower the freezing point of water by a non-colligative process. A 2% solution of antifreeze has a freezing point of — 1.2 °C and ice formed in their presence melts at — 0.02 °C. Measurements of antifreeze concentrations in ice indicate that these molecules, unlike other proteins of similar size and conformation, are incorporated into the solid phase during freezing and adsorb to it. Adsorption of the antifreezes to ice appears to inhibit growth along the preferred axes ( a -axes) by raising the curvature of the growth steps on the basal plane. At temperatures below — 1.2 °C, crystal growth occurs in the form of long spicules whose axes are parallel to the c -axis, the non-preferred axis of growth.

Structural variations in the alanine‐rich antifreeze proteins of the pleuronectinae

“…Each repeat represents almost three complete turns of a-helix organized such that the hydrophilic Thr and Asx side chains project on the same side of the helix from the first and second turns of each repeat. The model proposes that these hydrophilic groups hydrogen bond to the surface of microscopic ice crystals and thereby inhibit their growth along the preferred a axes [3]. In support of this model the 0.45-nm spacing between the Thr and Asx side chains matches the spacing between oxygen atoms in the ice lattice along the a axis.…”

A Diminished Role for Hydrogen Bonds in Antifreeze Protein Binding to Ice

“…It has always been assumed that Thr residues on winter flounder Type I AFP are largely responsible for ice binding. Their regular occupancy on one face of the helix suggests a lattice match mechanism and such a theory was advanced well before the availability of atomic resolution protein structures (3,35). However, the precise form of interaction of the hydroxyl with that of the ice water layer is not defined or understood.…”

“…It is reasonable to assume that the Thr adopt a similar rotameric state once they are bound to ice, since a random distribution of all possible Thr conformations would not produce the desired lattice matching distance of 16.7 Å. Regardless of the rotameric state of Thr, most computational studies place these residues above the water molecules that form the ridges of the {202 h1} surface (the {202 h1} surface has a regularly spaced ridge and valley topology) (8,10,12,35). This seems reasonable since short Thr side chain is probably not able to interact directly with those water molecules that lie in the valleys.…”

Structure‐function relationship in the globular type III antifreeze protein: Identification of a cluster of surface residues required for binding to ice

“…The difference in temperature between this nonequilibrium freezing point and the melting temperature is referred to as thermal hysteresis, the magnitude of which is a function of AFP concentration. DeVries and Lin (1977) and DeVries (1984) suggested that these antifreezes stop ice growth by adsorbing to specific ice planes via hydrogen bonds. This hypothesis remains central to all models proposed so far for antifreeze action.…”