Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada K7L 3N6.
J Mol Biol. 2012 Mar 9;416(5):713-24. doi: 10.1016/j.jmb.2012.01.032. Epub 2012 Jan 28.
The grass Lolium perenne produces an ice-binding protein (LpIBP) that helps this perennial tolerate freezing by inhibiting the recrystallization of ice. Ice-binding proteins (IBPs) are also produced by freeze-avoiding organisms to halt the growth of ice and are better known as antifreeze proteins (AFPs). To examine the structural basis for the different roles of these two IBP types, we have solved the first crystal structure of a plant IBP. The 118-residue LpIBP folds as a novel left-handed beta-roll with eight 14- or 15-residue coils and is stabilized by a small hydrophobic core and two internal Asn ladders. The ice-binding site (IBS) is formed by a flat beta-sheet on one surface of the beta-roll. We show that LpIBP binds to both the basal and primary-prism planes of ice, which is the hallmark of hyperactive AFPs. However, the antifreeze activity of LpIBP is less than 10% of that measured for those hyperactive AFPs with convergently evolved beta-solenoid structures. Whereas these hyperactive AFPs have two rows of aligned Thr residues on their IBS, the equivalent arrays in LpIBP are populated by a mixture of Thr, Ser and Val with several side-chain conformations. Substitution of Ser or Val for Thr on the IBS of a hyperactive AFP reduced its antifreeze activity. LpIBP may have evolved an IBS that has low antifreeze activity to avoid damage from rapid ice growth that occurs when temperatures exceed the capacity of AFPs to block ice growth while retaining the ability to inhibit ice recrystallization.
多年生黑麦草产生一种冰结合蛋白（LpIBP），通过抑制冰晶再结晶帮助这种多年生植物耐受冻结。抗冻蛋白（AFPs）也被避冻生物产生，以阻止冰的生长，并且更为人所知。为了研究这两种 IBP 类型的不同作用的结构基础，我们解决了第一个植物 IBP 的晶体结构。118 个残基的 LpIBP 折叠成一个新颖的左手β-螺旋，带有八个 14 或 15 个残基的线圈，并由一个小疏水性核心和两个内部 Asn 梯稳定。冰结合位点（IBS）由β-螺旋一侧的平 β-片层形成。我们表明，LpIBP 结合到冰的基底和初级棱柱面，这是超活性 AFP 的标志。然而，LpIBP 的抗冻活性不到那些具有趋同进化的β-螺线管结构的超活性 AFP 测量的 10%。虽然这些超活性 AFP 在其 IBS 上有两排对齐的 Thr 残基，但 LpIBP 的等效阵列由 Thr、Ser 和 Val 的混合物填充，并且几个侧链构象。在超活性 AFP 的 IBS 上用 Ser 或 Val 取代 Thr 会降低其抗冻活性。LpIBP 可能已经进化出一种低抗冻活性的 IBS，以避免在温度超过 AFP 阻止冰生长的能力时，由于快速冰生长而造成的损害，同时保留抑制冰晶再结晶的能力。
