Folding patterns of porin and bacteriorhodopsin.
Folding patterns of porin and bacteriorhodopsin.
复制标题
孔蛋白和细菌视紫红质的折叠模式。
作者：
C. Paul;J. Rosenbusch
孔蛋白横跨大肠杆菌的外膜，大部分蛋白质嵌入膜内。它缺乏明显的疏水结构域，主要由β -褶片组成。这些观测需要在低介电常数的环境中容纳极性和可电离残基。由于目前对膜蛋白结构约束的理解有限，提出了一种结构预测的最小方法，即识别导致多肽逆转其方向的片段（转向识别）。该方法的应用避免了疏水性参数，得到的孔蛋白模型与所有可用的实验数据吻合良好。极性残基和可电离残基在膜边界内的存在意味着氢键供体和受体基团的密集（饱和）网络。应用于疏水膜蛋白的范例，细菌视紫红质，揭示了其与α -螺旋折叠一致的模式。假设的结构在膜域中包含比先前假设的多得多的极性残基，这表明细菌视紫红质中也存在氢键网络。渗透蛋白质内部和表面的广泛网络可以解释两种蛋白质晶体阵列形成过程中功能单元之间的异常稳定性和紧密相互作用。
Porin spans the outer membrane of Escherichia coli with most of the protein embedded within the membrane. It lacks pronounced hydrophobic domains and consists predominantly of beta‐pleated sheet. These observations require the accommodation of polar and ionizable residues in an environment that has a low dielectric constant. Owing to a currently limited understanding of the constraints governing membrane protein structure, a minimal approach to structure prediction is proposed that identifies segments causing polypeptides to reverse their direction (turn identification). The application of this procedure avoids hydrophobicity parameters and yields a model of porin which is in good agreement with all experimental data available. The presence of polar and ionizable residues within membrane boundaries implies a dense (saturating) network of hydrogen bond donor and acceptor groups. Application to a paradigm of hydrophobic membrane proteins, bacteriorhodopsin, reveals a pattern consistent with its alpha‐helical folding. The postulated structure includes significantly more polar residues in the membrane domain than have been assumed previously, suggesting that there are also hydrogen bonding networks in bacteriorhodopsin. Extensive networks permeating protein interior and surfaces would explain the extraordinary stability and the tight interactions between functional units in the formation of crystalline arrays of both proteins.