Wen D, Laursen R A
Department of Chemistry, Boston University, Massachusetts 02215.
J Biol Chem. 1992 Jul 15;267(20):14102-8.
An alanine-rich, alpha-helical antifreeze polypeptide (AFP) from the winter flounder and seven analogs with variations in the arrangement of neutral, polar amino acids were synthesized. Circular dichroism studies determined that all of the peptides, except for one containing a proline residue, were essentially 100% alpha-helical. Freezing point depression data, analyzed by three methods, showed that rearrangement of polar residues resulted in moderate to complete loss of anti-freeze activity. It was observed that ice crystals grow as hexagonal bipyramids in dilute solutions, with a constant c to alpha axis ratio of about 3.3. Above a critical threshold concentration, which may depend on the AFP to ice binding constant and reflect the onset of cooperative interactions, growth ceases until the temperature is lowered to the freezing point. We conclude that a specific arrangement of both threonine and asparagine (or aspartic acid) residues is critical for maximal activity and that the AFPs probably bind to the pyramidal faces of ice with a specific orientation. These conclusions are consistent with a recent report (Knight, C. A., Cheng, C. C., and DeVries, A. L. (1991) Biophys. J. 59, 409-418) that a similar AFP adsorbs to the [2021] pyramidal planes of ice in dilute solution.
合成了一种来自冬鲽的富含丙氨酸的α-螺旋抗冻多肽（AFP）以及七种中性、极性氨基酸排列方式不同的类似物。圆二色性研究表明，除了一种含有脯氨酸残基的肽段外，所有肽段基本上100%呈α-螺旋结构。通过三种方法分析的冰点降低数据表明，极性残基的重排导致抗冻活性中度至完全丧失。观察到冰晶在稀溶液中以六方双锥体形式生长，c轴与α轴的恒定比例约为3.3。高于临界阈值浓度（这可能取决于AFP与冰的结合常数并反映协同相互作用的开始），生长停止，直到温度降至冰点。我们得出结论，苏氨酸和天冬酰胺（或天冬氨酸）残基的特定排列对于最大活性至关重要，并且AFP可能以特定方向结合到冰的锥面上。这些结论与最近的一份报告（Knight, C. A., Cheng, C. C., and DeVries, A. L. (1991) Biophys. J. 59, 409 - 418）一致，即一种类似的AFP在稀溶液中吸附到冰的[2021]锥面上。
