A natural variant of type I antifreeze protein with four ice-binding repeats is a particularly potent antifreeze. |
| |
| Authors: | H. Chao R. S. Hodges C. M. Kay S. Y. Gauthier P. L. Davies |
| |
| Affiliation: | Protein Engineering Network of Centres of Excellence, University of Alberta, Edmonton, Canada. |
| |
| Abstract: | 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. |
| |
| Keywords: | |
|
|
