Role of the IXI/V motif in oligomer assembly and function of StHsp 14.0, a small heat shock protein from the acidothermophilic archaeon, Sulfolobus tokodaii strain 7
Role of the IXI/V motif in oligomer assembly and function of StHsp 14.0, a small heat shock protein from the acidothermophilic archaeon, Sulfolobus tokodaii strain 7
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DOI：
10.1002/prot.21762
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发表时间：
2008-05-01
影响因子：
2.9
通讯作者：
Yohda, Masafumi
中科院分区：
文献类型：
--
作者：
Saji, Hitoshi;Iizuka, Ryo;Yohda, Masafumi
小热休克蛋白（sHsps）是最普遍存在的分子伴侣之一。它们根据一个保守的结构域——α -结晶蛋白结构域——分组在一起。通常，sHsps以9-40个亚基的低聚物存在，低聚物经过可逆的温度依赖解离成更小的二聚体，与变性底物蛋白相互作用。先前的研究表明，c端区域，特别是公认的IXI/V基序，负责低聚物的组装。在这项研究中，我们检测了嗜酸嗜热古菌Sulfolobus tokodaii菌株7中StHsp14.0寡聚体组装和功能c端区域的缺失或突变。突变的StHsp14.0基因c端缺失或IXI/V基序中的He残基被Ala、Ser或Phe残基取代，不能形成大的低聚物，并失去伴侣活性。StHsp14.0WKW的IXI/V基序中的Ile残基变为Tip，与野生型相似，以低聚物的形式存在。然而，它解离成小的低聚物，并在相对较低的温度下表现出伴侣活性。基序中的两个Ile残基被替换为相对较小的Ala或Ser残基，也导致富β -sheet二级结构的改变和疏水性的降低。有趣的是，氨基酸替换为Phe的StHsp14.0突变体虽然不能形成寡聚体结构，但二级结构几乎保持不变，疏水性相对较高。结果表明，c端IXI/V基序氨基酸的疏水性和大小不仅对低聚物的组装起作用，而且对维持富含β -sheet的二级结构和疏水性起重要作用，这对sHsp的功能至关重要。
Small heat shock proteins (sHsps) are one of the most ubiquitous molecular chaperones. They are grouped together based on a conserved domain, the alpha-crystallin domain. Generally, sHsps exist as oligomers of 9-40 subunits, and the oligomers undergo reversible temperature-dependent dissociation into smaller species as dimers, which interact with denaturing substrate proteins. Previous studies have shown that the C-terminal region, especially the consensus IXI/V motif, is responsible for oligomer assembly. In this study, we examined deletions or mutations in the C-terminal region on the oligomer assembly and function of StHsp14.0, an sHsp from an acidothermophilic archaeon, Sulfolobus tokodaii strain 7. Mutated StHsp14.0 with C-terminal deletion or replacement of He residues in the IXI/V motif to Ala, Ser, or Phe residues could not form large oligomers and lost chaperone activity. StHsp14.0WKW, whose Ile residues in the IXI/V motif are changed to Tip, existed as an oligomer like that of the wild type. However, it dissociates to small oligomers and exhibits chaperone activity at relatively lowered temperature. Replacement of two Ile residues in the motif to relatively small residues, Ala or Ser, also resulted in the change of beta-sheet rich secondary structure and decrease of hydrophobicity. Interestingly, StHsp14.0 mutant with amino acid replacements to Phe kept almost the same secondary structure and relatively high hydrophobicity despite that it could not form an oligomeric structure. The results show that hydrophobicity and size of the amino acids in the IXI/V motif in the C-terminal region are responsible not only for assembly of the oligomer but also for the maintenance of beta-sheet rich secondary structure and hydrophobicity, which are important for the function of sHsp.