Conformational transitions of membrane-spanning peptides

嵌入膜中的蛋白质构成了人类基因组的三分之一。它们调节生物膜上的分子交通和信息流，因此，它们是研究和/或调节活细胞过程的有吸引力的生物分子。据估计，目前大约70%的药物靶点是膜蛋白。然而，目前在蛋白质数据库中沉积的bbbb56000个结构中，膜蛋白只占1-2%，部分原因是这些高度疏水分子的纯化和结构表征方面存在技术挑战。幸运的是，对膜蛋白折叠的深入了解并不完全依赖于高分辨率结构的可用性，而是通过生产单个跨膜（TM）序列作为合成肽来促进。这些肽模型的优势在于它们能够复制天然的螺旋-螺旋接触，能够产生足够数量的结构分析，并且能够通过各种生物物理技术进行研究。我们在这里提出了一系列的实验，在这些原理的基础上，研究细胞机器识别TM片段的结构和序列决定因素；评价跨膜肽侧链化学对膜插入和折叠的影响；并利用带有His残基标记的膜跨越肽来筛选膜蛋白伴侣。通过合理设计肽序列和选择合适的膜模拟介质，在这些肽中观察到的螺旋-螺旋相互作用可能非常接近其天然结构中的TM结构域相互作用。结果将有助于定义膜蛋白折叠中结构-功能关系的关键原则，并在更长远的范围内，提供有关这些因素如何在疾病状态下变得异常的见解。

Proteins embedded in membranes comprise fully one-third of the human genome. They regulate the molecular traffic and information flow across biological membranes and, as such, represent attractive biomolecules for the study and/or modulation of processes in living cells. It is estimated that approximately 70% of all current pharmaceutical targets are membrane proteins. Yet membrane proteins currently represent 1-2% of the >56000 structures deposited in the Protein Data Bank, in part because of the technical challenges associated with the purification, and structural characterization of these highly hydrophobic molecules. Fortunately, gaining insight into membrane protein folding has not relied exclusively on the availability of high-resolution structures, but has been facilitated by the production of individual transmembrane (TM) sequences as synthetic peptides. The advantages of these peptide models lie in their ability to replicate native helix-helix contacts, to be produced in sufficient quantities for structural analysis, and in their amenability to studies by a variety of biophysical techniques. We propose here a series of experiments where these principles are implemented to investigate structure and sequence determinants of TM segment recognition by cellular machinery; to evaluate how the side chain chemistry of membrane-spanning peptides contributes to membrane insertion and folding; and to use membrane spanning peptides tagged with His residues to screen for membrane protein partners. In concert with the judicious design of peptide sequences and choice of appropriate membrane-mimetic media, the helix-helix interactions observed in these peptides may be expected to closely approximate the TM domain interactions in their native structures. Results will help define key principles about structure-function relationships in membrane protein folding, and in the longer range, provide insights as to how these factors become aberrant in disease states.