Mechanism of Cis-Inhibition of PolyQ Fibrillation by PolyP: PPII Oligomers and the Hydrophobic Effect
Mechanism of Cis-Inhibition of PolyQ Fibrillation by PolyP: PPII Oligomers and the Hydrophobic Effect
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DOI：
10.1016/j.bpj.2009.07.062
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发表时间：
2009-10-21
影响因子：
3.4
通讯作者：
Meredith, Stephen C.
中科院分区：
文献类型：
--
作者：
Darnell, Gregory D.;Derryberry, JohnMark;Meredith, Stephen C.
PolyQ肽在聚脯氨酸II（PPII）和β折叠构象之间摇摆不定。在串联的聚Q-聚P肽中，聚P片段使平衡向PPII倾斜，增加了原纤化所需的Gln残基的阈值数量。为了研究polyP侧翼片段对polyQ纤维化的顺式抑制机制，我们检查了短polyQ、polyP和串联polyQ-polyP肽。这些polyQ肽只有三个谷氨酰胺，不能形成β折叠原纤维。我们证明了polyQ-聚P肽在高浓度下形成具有PPII结构的小的可溶性低聚物（如尺寸排阻色谱和扩散系数测量所示）（如圆二色谱和（3）来自恒定时间相关光谱NMR的Gln残基的J（HN-C α）常数所示）。核Overhauser效应光谱和分子建模表明，这些肽的自缔合发生作为疏水和空间效应的结果。Pro侧链向溶剂呈现三个亚甲基，通过疏水效应有利于聚P的自缔合。具有两个亚甲基的Gin侧链可以采用类似于Pro侧链的构象，也允许通过疏水效应自缔合。此外，Gln和Pro侧链与polyQ片段的C-末端侧之间的空间冲突有利于在polyQ片段中采用PPII样结构。polyQ片段的构象适应性允许polyP片段对蛋白质如亨廷顿蛋白中的polyQ片段的原纤化的顺式抑制作用。
PolyQ peptides teeter between polyproline II (PPII) and beta-sheet conformations. In tandem polyQ-polyP peptides, the polyP segment tips the balance toward PPII, increasing the threshold number of Gin residues needed for fibrillation. To investigate the mechanism of cis-inhibition by flanking polyP segments on polyQ fibrillation, we examined short polyQ, polyP, and tandem polyQ-polyP peptides. These polyQ peptides have only three glutamines and cannot form beta-sheet fibrils. We demonstrate that polyQ-polyP peptides form small, soluble oligomers at high concentrations (as shown by size exclusion chromatography and diffusion coefficient measurements) with PPII structure (as shown by circular dichroism spectroscopy and (3)J(HN-C alpha) constants of Gin residues from constant time correlation spectroscopy NMR). Nuclear Overhauser effect spectroscopy and molecular modeling suggest that self-association of these peptides occurs as a result of both hydrophobic and steric effects. Pro side chains present three methylenes to solvent, favoring self-association of polyP through the hydrophobic effect. Gin side chains, with two methylene groups, can adopt a conformation similar to that of Pro side chains, also permitting self-association through the hydrophobic effect. Furthermore, steric clashes between Gin and Pro side chains to the C-terminal side of the polyQ segment favor adoption of the PPII-Iike structure in the polyQ segment. The conformational adaptability of the polyQ segment permits the cis-inhibitory effect of polyP segments on fibrillation by the polyQ segments in proteins such as huntingtin.