A parallel coiled-coil tetramer with offset helices
A parallel coiled-coil tetramer with offset helices
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DOI：
10.1021/bi061914m
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发表时间：
2006-12-26
期刊：
影响因子：
2.9
通讯作者：
Lu, Min
中科院分区：
文献类型：
--
作者：
Liu, Jie;Deng, Yiqun;Lu, Min
特定的螺旋-螺旋相互作用是组装蛋白质天然状态和蛋白质-蛋白质界面的基础。螺旋线圈为阐明α螺旋之间的分子识别原理提供了一个独特的模型系统。螺旋卷曲折叠是由在第一(A)和第四(D)位含有疏水残基的特征七个氨基酸重复指定的。相隔3个和4个残基的非极性侧链称为3-4疏水重复序列。E或g位的非极性氨基酸(对应于3-3-1疏水重复)的存在可以为紧密堆积α-螺旋提供新的可能性，其中包括例如lac抑制物四聚结构域。在这里，我们证明了一个史无前例的盘绕-线圈界面的结果是二聚体GCN4亮氨酸拉链中e位的三个带电残基被非极性的valine侧链取代。平衡圆二色谱和分析超速离心法研究表明，含有缬氨酸的突变体形成了一个离散的α-螺旋四聚体，其稳定性明显高于母体亮氨酸拉链分子。四聚体的1.35埃分辨率的晶体结构揭示了一个平行的四股螺旋线圈，具有三个残基的螺旋间距。四聚体构象中三个疏水位置的局部堆积几何构型与经典四聚体结构完全不同，但与三股螺旋结构中的堆积几何形状相似。这些研究表明，在a和d侧链之外的不同范德华相互作用可以产生一组不同的螺旋-螺旋界面和三维超螺旋结构。
Specific helix-helix interactions are fundamental in assembling the native state of proteins and in protein-protein interfaces. Coiled coils afford a unique model system for elucidating principles of molecular recognition between alpha helices. The coiled-coil fold is specified by a characteristic seven amino acid repeat containing hydrophobic residues at the first (a) and fourth (d) positions. Nonpolar side chains spaced three and four residues apart are referred to as the 3-4 hydrophobic repeat. The presence of apolar amino acids at the e or g positions (corresponding to a 3-3-1 hydrophobic repeat) can provide new possibilities for close-packing of alpha-helices that includes examples such as the lac repressor tetramerization domain. Here we demonstrate that an unprecedented coiled-coil interface results from replacement of three charged residues at the e positions in the dimeric GCN4 leucine zipper by nonpolar valine side chains. Equilibrium circular dichroism and analytical ultracentrifugation studies indicate that the valine-containing mutant forms a discrete alpha-helical tetramer with a significantly higher stability than the parent leucine-zipper molecule. The 1.35 angstrom resolution crystal structure of the tetramer reveals a parallel four-stranded coiled coil with a three-residue interhelical offset. The local packing geometry of the three hydrophobic positions in the tetramer conformation is completely different from that seen in classical tetrameric structures yet bears resemblance to that in three-stranded coiled coils. These studies demonstrate that distinct van der Waals interactions beyond the a and d side chains can generate a diverse set of helix-helix interfaces and three-dimensional supercoil structures.