Membrane Anchoring of α-Helical Proteins: Role of Tryptophan.
Membrane Anchoring of α-Helical Proteins: Role of Tryptophan.
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α-螺旋蛋白的膜锚定：色氨酸的作用。
DOI：
10.1021/acs.jpcb.7b11227
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Ulmer,TobiasS
中科院分区：
文献类型：
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作者：
Situ,AlanJ;Kang,So-Min;Frey,BenjaminB;An,Woojin;Kim,Chungho;Ulmer,TobiasS
膜蛋白的功能依赖于蛋白质相对于脂质的特定取向。与蛋白质锚定明显相关，色氨酸残基在脂质头群区域富集。为了表征α-螺旋膜蛋白中这种关系的热力学和结构基础，我们研究了三种保守的色氨酸在磷脂小细胞和哺乳动物膜中异二聚体整合素α ib β3跨膜（TM）复合物折叠中的作用。在单倍体的均质脂环境中，色氨酸被极性不同的残基所替代。色氨酸周围的静电电位引导了合适的极性，这表明色氨酸可以通过调节其各向异性侧链的方向来补充不同的环境，从而实现位点特异性锚定。色氨酸作为唯一的膜锚，对TM复合物在单胞体中的稳定性贡献为0.4 kcal/mol。在膜中，即使用酪氨酸替代色氨酸也更加困难，这表明与生物膜的异质脂质相互作用的能力更强。有趣的是，在整合素激活启动的细胞内TM螺旋末端，发现通过相反极性模式与脂质相互作用的序列基序限制了色氨酸锚定之外的TM螺旋方向。与双胞体相比，苯丙氨酸成为膜中最不被接受的替代品，表明疏水效应的作用增加。总之，我们的研究表明，色氨酸广泛的两亲性范围、膜复杂性和疏水效应是色氨酸膜锚定的重要因素。
The function of membrane proteins relies on a defined orientation of protein relative to lipid. In apparent correlation to protein anchoring, tryptophan residues are enriched in the lipid headgroup region. To characterize the thermodynamic and structural basis of this relationship in α-helical membrane proteins, we examined the role of three conserved tryptophans in the folding of the heterodimeric integrin αIIbβ3 transmembrane (TM) complex in phospholipid bicelles and mammalian membranes. In the homogenous lipid environment of bicelles, tryptophan was replaceable by residues of distinct polarities. The appropriate polarity was guided by the electrostatic potential of the tryptophan surrounding, suggesting that tryptophan can complement diverse environments by adjusting the orientation of its anisotropic side chain to achieve site-specific anchoring. As a sole membrane anchor, tryptophan made a contribution of 0.4 kcal/mol to TM complex stability in bicelles. In membranes, it proved more difficult to replace tryptophan even by tyrosine, indicating a superior capacity to interact with heterogeneous lipids of biological membranes. Interestingly, at intracellular TM helix ends, where integrin activation is initiated, sequence motifs that interact with lipids via opposing polarity patterns were found to restrict TM helix orientations beyond tryptophan anchoring. In contrast to bicelles, phenylalanine became the least accepted substitute in membranes, demonstrating an increased role of the hydrophobic effect. Altogether, our study implicates a wide amphiphilic range of tryptophan, membrane complexity, and the hydrophobic effect to be important factors in tryptophan membrane anchoring.