聚脯氨酸螺旋
抗冻蛋白
基因亚型
反平行(数学)
化学
圆二色性
防冻剂
生物化学
结晶学
生物
肽
立体化学
基因
物理
磁场
有机化学
量子力学
作者
Yee-Foong Mok,Feng-Hsu Lin,Laurie A. Graham,Yeliz Celik,Ido Braslavsky,Peter L. Davies
出处
期刊:Biochemistry
[American Chemical Society]
日期:2010-03-01
卷期号:49 (11): 2593-2603
被引量:60
摘要
The snow flea (Hypogastrum harveyi) is protected from freezing at sub-zero temperatures by a glycine-rich antifreeze protein (AFP) that binds to seed ice crystals and prevents them from growing larger. This AFP is hyperactive and comprises two isoforms [Graham, L. A., and Davies, P. L. (2005) Science 310, 461]. The larger isoform (15.7 kDa) exhibits several-fold higher activity than the smaller isoform (6.5 kDa), although it is considerably less abundant. To establish the molecular basis for this difference in activity, we determined the sequence of the large isoform. The primary sequences of these two isoforms are surprisingly divergent. However, both contain tripeptide repeats and turn motifs that enabled us to build a three-dimensional model of the large isoform based upon the six-polyproline helix structure of the small isoform. Our model contains 13 polyproline type II helices connected by proline-containing loops stacked into two flat sheets oriented antiparallel to one another. The structure is strictly amphipathic, with a hydrophilic surface on one side and a hydrophobic, putative ice-binding surface on the other. The putative ice-binding site is approximately twice as large in area as that of the small isoform, providing an explanation for the difference in activity that is consistent with other examples noted. By tagging the recombinant AFP with green fluorescent protein, we observed its binding to multiple planes of ice, especially the basal plane. This finding supports the correlation between AFP hyperactivity and basal plane binding first observed with spruce budworm AFP.
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