Fully active QAE isoform confers thermal hysteresis activity on a defective SP isoform of type III antifreeze protein
Fully active QAE isoform confers thermal hysteresis activity on a defective SP isoform of type III antifreeze protein
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完全活性的 QAE 异构体赋予 III 型抗冻蛋白缺陷 SP 异构体热滞活性
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
S. Tsuda
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作者：
Manabu Takamichi;Y. Nishimiya;A. Miura;S. Tsuda
III型抗冻蛋白天然表达为磺丙基-葡聚糖(SP)和季氨乙基-葡聚糖结合亚型，其序列同源性约为55%。我们研究了SP亚型(NFeAFP_6)和QAE亚型(NFeAFP_8)的结冰特性，这两种亚型都是从日本鱼Zoarces langatus Kner中鉴定出来的。这两种异构体具有冰形成能力，如形成冰双金字塔，但nFeAFP6不能阻止晶体生长，也没有表现出热滞活性。例如，当测量0.1 mm蛋白质溶液在低于熔点0.25 °C时，nFeAFP 6的冰生长速度是nFeAFP 8的1 000倍。然而，当只有1%的 = 存在时，nFeAFP 6表现出完全的热滞活性(即[nFeAFP 8]/[nFeAFP 6]nFeAFP6 0.01)，其有效性与单独使用nFeAFP 8的效果没有区别。我们还观察到，随着温度的降低，两种异构体的冰晶都从冰双金字塔的顶端突然长大。这些结果表明，添加微量的活性异构体可以恢复缺乏活性成分的抗冻蛋白异构体的冰生长抑制活性。
Type III antifreeze protein is naturally expressed as a mixture of sulfopropyl‐Sephadex (SP) and quaternary aminoethyl‐Sephadex (QAE)‐binding isoforms, whose sequence identity is approximately 55%. We studied the ice‐binding properties of a SP isoform (nfeAFP6) and the differences from those of a QAE isoform (nfeAFP8); both of these isoforms have been identified from the Japanese fish Zoarces elongatus Kner. The two isoforms possessed ice‐shaping ability, such as the creation of an ice bipyramid, but nfeAFP6 was unable to halt crystal growth and exhibited no thermal hysteresis activity. For example, the ice growth rate for nfeAFP6 was 1000‐fold higher than that for nfeAFP8 when measured for 0.1 mm protein solution at 0.25 °C below the melting point. Nevertheless, nfeAFP6 exhibited full thermal hysteresis activity in the presence of only 1% nfeAFP8 (i.e. [nfeAFP8]/[nfeAFP6] = 0.01), the effectiveness of which was indistinguishable from that of nfeAFP8 alone. We also observed a burst of ice crystal growth from the tip of the ice bipyramid for both isoforms on lowering the temperature. These results suggest that the ice growth inhibitory activity of an antifreeze protein isoform lacking the active component is restored by the addition of a minute amount of the active isoform.