Chao H, Hodges R S, Kay C M, Gauthier S Y, Davies P L
Protein Engineering Network of Centres of Excellence, University of Alberta, Edmonton, Canada.
Protein Sci. 1996 Jun;5(6):1150-6. doi: 10.1002/pro.5560050617.
A 4.3-kDa variant of Type I antifreeze protein (AFP9) was purified from winter flounder serum by size exclusion chromatography and reversed-phase HPLC. By the criteria of mass, amino acid composition, and N-terminal sequences of tryptic peptides, this variant is the posttranslationally modified product of the previously characterized AFP gene 21a. It has 52 amino acids and contains four 11-amino acid repeats, one more than the major serum AFP components. The larger protein is completely alpha-helical at 0 degree C, with a melting temperature of 18 degrees C. It is considerably more active as an antifreeze than the three-repeat winter flounder AFP and the four-repeat yellowtail flounder AFP, both on a molar and a mg/mL basis. Several structural features of the four-repeat winter flounder AFP, including its larger size, additional ice-binding residues, and differences in ice-binding motifs might contribute to its greater activity. Its abundance in flounder serum, together with its potency as an antifreeze, suggest that AFP9 makes a significant contribution to the overall freezing point depression of the host.
通过尺寸排阻色谱法和反相高效液相色谱法从冬鲽血清中纯化出一种4.3千道尔顿的I型抗冻蛋白变体（AFP9）。根据胰蛋白酶肽段的质量、氨基酸组成和N端序列标准，该变体是先前鉴定的AFP基因21a的翻译后修饰产物。它有52个氨基酸，包含四个11个氨基酸的重复序列，比主要的血清AFP成分多一个。这种较大的蛋白质在0℃时完全呈α螺旋结构，解链温度为18℃。无论是以摩尔为基础还是以毫克/毫升为基础，它作为抗冻剂的活性都比三重复序列的冬鲽AFP和四重复序列的黄尾鲽AFP高得多。四重复序列的冬鲽AFP的几个结构特征，包括其更大的尺寸、额外的冰结合残基以及冰结合基序的差异，可能导致其活性更高。它在鲽血清中的丰度及其作为抗冻剂的效力表明，AFP9对宿主的整体冰点降低有显著贡献。
