Deng G, Laursen R A
Department of Chemistry, Boston University, Boston, MA 02215, USA.
Biochim Biophys Acta. 1998 Nov 10;1388(2):305-14. doi: 10.1016/s0167-4838(98)00180-0.
A new type of antifreeze protein was isolated from the serum of the longhorn sculpin, Myoxocephalus octodecimspinosis, by gel filtration and high-performance liquid chromatography. This protein (LS-12) exhibits freezing point depression activity (thermal hysteresis) and ice crystal modification properties similar to those seen for other types of fish antifreeze polypeptide, except that ice crystals grow as hexagonal trapezohedra in the presence of LS-12, rather than hexagonal bipyramids usually seen. Ice crystal etching studies demonstrate that LS-12 does not bind to the hexagonal bipyramidal or secondary prism surfaces reported for the antifreeze polypeptides from winter flounder and shorthorn sculpin, respectively. Circular dichroism studies indicate that LS-12 has an alpha-helix content of about 60% at 1 degreesC, which is in good agreement with a value of about 70% predicted from the amino acid sequence. Limited proteolysis studies and further analysis of the amino acid sequence suggest that LS-12 consists of four amphipathic alpha-helices of similar length which are folded into a four-helix bundle. Based on its size (Mr=12299) and predicted tertiary structure, LS-12 can be regarded as the first example of a new class (type IV) of fish antifreeze protein.
通过凝胶过滤和高效液相色谱法，从长角杜父鱼（Myoxocephalus octodecimspinosis）的血清中分离出一种新型抗冻蛋白。这种蛋白（LS-12）表现出冰点降低活性（热滞）和冰晶修饰特性，与其他类型的鱼类抗冻多肽相似，不同的是，在LS-12存在的情况下，冰晶以六方偏方三八面体的形式生长，而不是通常所见的六方双锥体。冰晶蚀刻研究表明，LS-12并不分别结合于冬鲽和短角杜父鱼抗冻多肽所报道的六方双锥体或次生棱柱表面。圆二色性研究表明，在1℃时，LS-12的α-螺旋含量约为60%，这与根据氨基酸序列预测的约70%的值非常吻合。有限的蛋白水解研究和对氨基酸序列的进一步分析表明，LS-12由四个长度相似的两亲性α-螺旋组成，这些螺旋折叠成一个四螺旋束。基于其大小（Mr=12299）和预测的三级结构，LS-12可被视为鱼类抗冻蛋白新类别（IV型）的首个实例。
