Miick S M, Casteel K M, Millhauser G L
Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
Biochemistry. 1993 Aug 10;32(31):8014-21. doi: 10.1021/bi00082a024.
The alanine-based 3K(I) peptide is reported to be very helical in aqueous solution. We have prepared a series of six nitroxide spin labeled analogs of the 3K(I) sequence and measured the variable-temperature ESR spectra for each in order to reveal the position-dependent peptide dynamics. From analysis of these local dynamics under helix-forming conditions at 1 degree C, we find that the helix termini show greater local dynamics than the peptide cancer. Further, the C-terminus is more mobile than the N-terminus. Even in the helix-promoting solvent trifluoroethanol, the results indicate that there is still substantially greater dynamics at the helix termini than at the peptide center. The unfolded state is also investigated, and we find that the peptide unfolded by guanidine hydrochloride is somewhat different than that found for high-temperature aqueous solution. Recently it was suggested that short 16-mer peptides may adopt a 3(10)-helix structure instead of the expected alpha-helix. The data presented here at 1 degree C show that there is sufficient disorder within the peptide to accommodate the 3(10) structure. Also calculated are the backbone torsional fluctuations, and the results compare well to those from computer molecular dynamics studies. A proposal is outlined that explains how the enhanced dynamics found at the C-terminus results from the exposure of the helix hydrogen bonds to aqueous solvent in this region of the peptide.
据报道，基于丙氨酸的3K(I)肽在水溶液中具有很高的螺旋性。我们制备了一系列3K(I)序列的六种氮氧化物自旋标记类似物，并测量了每种类似物的变温电子顺磁共振（ESR）光谱，以揭示肽动力学的位置依赖性。通过在1℃的螺旋形成条件下对这些局部动力学进行分析，我们发现螺旋末端比肽中心表现出更大的局部动力学。此外，C末端比N末端更具流动性。即使在促进螺旋的溶剂三氟乙醇中，结果表明螺旋末端的动力学仍然比肽中心大得多。我们还研究了未折叠状态，发现盐酸胍展开的肽与高温水溶液中的肽有所不同。最近有人提出，短的16聚体肽可能采用3(10)-螺旋结构而不是预期的α-螺旋结构。这里在1℃给出的数据表明，肽内存在足够的无序以容纳3(10)结构。我们还计算了主链扭转波动，结果与计算机分子动力学研究的结果比较吻合。本文概述了一项提议，解释了在肽的该区域中螺旋氢键暴露于水性溶剂如何导致C末端发现的增强动力学。
