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KMID : 0613820170270050584
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Journal of Life Science
2017 Volume.27 No. 5 p.584 ~ p.590
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Antifreeze Activity of Dimerized Type I Antifreeze Protein Fragments
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Kim Hak-Jun
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Abstract
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Antifreeze proteins (AFPs) bind to ice crystals and inhibit their growth. AFPs are essential for the survival of organisms living in subzero environments. Type I AFP (AFP37) isolated from winter flounder is an α-helical peptide of 37 residues long. In this study, we attempted to develop short AFP fragments with higher activity and solubility. We designed and synthesized N-terminal 15 and 21 residue-long AFPs, designated AFP15 and 21. Also dimerized AFP15 and 21, designated dAFP15N and dAFP21N, respectively, were generated through disulfide bonds between peptides containing CGG residues added to the N-terminus of AFP15 and AFP21 (designated AFP15N and 21N). Their helical contents and antifreeze activities were assessed using circular dichroism (CD) spectroscopy and a nanoliter osmometer, respectively. The helical content of AFP15 AFP21, AFP15N, AFP21N, dAFP15N and dAFP21N was 47, 48, 23.8, 28, 49.1, and 52%, respectively compared to that of wild type AFP37; the antifreeze activity was 8.4, 9.3, 0.05, 5.6, 12.1, 11.2% respectively, compared to that of wild type AFP37. Contrary to our anticipation, the dimerized peptides showed almost the same antifreeze activity as their monomeric counterparts. These results indicate that the dimerized peptides behave as monomeric peptides due to the high rotational freedom of disulfide bonds connecting two monomeric peptides. The star-shaped ice crystals generated by the peptides also demonstrated weak interaction between ice and peptides.
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KEYWORD
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Antifreeze protein, circular dichroism, dimerization, thermal hysteresis, winter flounder
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