Flounder AFP

Ananthanarayanan and Hew (35) have shown through circular dichroism measurements that flounder AFP possesses a large proportion ( 85%) of an a-helical conformation at a low temperature (— 1°C). The helical content decreases as the temperature rises. Viscosity data at — 1°C indicate an asymmetrical shape for the protein molecule compatible with its high helical content. The data for circular dichroism has recently been confirmed (36). No data is available concerning the assumption that this highly helical structure at — 1°C is related to its function. 

Figure 22 shows a single snapshot of the coordinates for the ice/AFP/water after 200 ps of total simulation time. In Figure 22 notice that the a-helix is more well-defined than it was at the beginning of the simulation (See Figure 21). The helicity was determined using the DSSP algorithm in RasMol 2.6[32]. The THR residues are in a line and remain spaced approximately 16.7 A apart. Finally it appears that the helix bends to follow the contour of the ice/water interface. This bending of the winter flounder AFP was observed in the molecular dynamics simulations of McDonald et al. [33] and Jorgensen et al. [34]. Merz et al. [35, 36] have published two papers, one on the dynamics of a Type I antifreeze protein in water using an NPT dynamics method and a second paper where they place a shell of liquid water over the antifreeze protein bound to ice. Unfortunately at this time we have not been able to fully characterize the ice/water interface in this simulation or perform any other necessary analysis. It is clear that additional simulations at the ice/water interface are necessary and that the results of these simulations will provide a clear molecular explanation of AFP binding at the ice/water interlace.

The winter flounder antifreeze protein (AFP), characterized by Sicheri and Yang [42], consists of 37 residues of eight amino acids in an a-helix configuration. The AFP protein was synthesized by the conjoining of the Aa residues determined in the glycine mold, with the exception of the two residues at each of the termini, FIOOC-Asp Thr and Ala Arg-NP and the synthesized protein fragment is left with open amidic surfaces on the... 

Fig. 7.6 The 33-residue fragment of the winter flounder antifreeze protein (AFP), constructed by the conjoining of the Aa amino acid residues defined within the glycine mold , pictured in terms of its 0.001 au isodensity envelope, its van der Waals envelope. This is a view showing the ice-binding motif. It is believed that the AFP strand binds... 

AFPs Antifreeze proteins (from winter flounder) BP/Shell (Edwards, 1994) ... 

Figure 7.42. Model for regulation of AFP synthesis in winter flounder (Pleuronectes americanus). CNS central nervous system GHRH growth hormone releasing hormone GH growth hormone IGF-1 insulin-like growth factor-1 C/EBPa CCAAT enhancer binding protein a AEP antifreeze enhancerbinding protein. See text for details. Arrows with striped tails denote up-regulation or down-regulation.

Finally, it is necessary to emphasize that, owing to the scarcity of data on the physical characterization of the flounder and the synthetic AFP systems, all these ideas are still awaiting more conclusive evidence. In particular, the degree of antifreeze activity in the AFGP, the AFP, and the synthetic AFP are different. Is there a variation of degrees of one antifreeze mechanism, or is there more than one basic mechanism of antifreeze and saturation of the antifreeze function ... 

Purified Type I fish AFP from winter flounder (wfAFP) was kindly provided by A/F Protein Canada Inc. Dr. E. D. Sloan (Colorado School of Mines, USA) kindly provided the PVP (30K) sample. The wfAFP and PVP solutions were prepared with ultrapure water (18.2 mQ cm at 298K, produced by Milli-Qd) ultrapure water purification systems, Millipore, Billerica, U.S.A.) directly at 25.0 pM. Samples were assessed for their ability to adsorb to Si02 or polystyrene (PS). 

Anti-freeze protein type 1 (AFP) Platichthys spp. (flounder) Multiple freeze-thaw cycles, pH 4 or 7 (Graether et al. 2003)... 

Antifreeze polypeptides are found in the blood plasma of bony fishes from the polar and subpolar oceans. The major antifreeze polypeptide (AFP) from winter flounder (37 amino acid residues) is a single alpha-helix [18]. 

---