FTIR spectroscopy of alanine-based peptides: assignment of the amide I' modes for random coil and helix.
FTIR spectroscopy of alanine-based peptides: assignment of the amide I' modes for random coil and helix.
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DOI：
10.1006/jsbi.1995.1002
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发表时间：
1995
影响因子：
3
通讯作者：
G. Martinez;G. Millhauser
中科院分区：
文献类型：
--
作者：
G. Martinez;G. Millhauser
傅里叶变换红外 (FTIR) 光谱已用于探索三种螺旋丙氨酸肽的热解折叠。每个肽都遵循通用序列 Ac-(AAAX)nA-NH2，其中 X 是 Lys+ 或 Arg+，n = 3 或 4。选择这些特定的肽是因为它们含有不同数量的 3(10)- 和 α-螺旋。在螺旋形成条件下，所有三种肽的酰胺 I' 带均在 1632 至 1635 cm-1 之间。这些结果与蛋白质中 α 螺旋的分配不一致，其中酰胺 I' 带通常位于 1650 cm-1 以上。在高温下，所有肽均表现出 1642 cm-1 的酰胺 I' 带，这是无规卷曲的公认值。 4K 肽（n = 4，X = Lys+）的可变温度光谱是 1 摄氏度下三种肽中 α 螺旋最多的肽，它揭示了一个等吸光点，表明存在协同的二态展开转变。然而，其他肽没有显示出等吸光点，从而表明沿着热解折叠途径存在中间体，可能是 3(10)-螺旋。
Fourier transform infrared (FTIR) spectroscopy has been used to explore the thermal unfolding of three helical, alanine-based peptides. Each of the peptides follows the general sequence Ac-(AAAX)nA-NH2 where X is either Lys+ or Arg+ and n = 3 or 4. These particular peptides were chosen because they contain varying amounts of 3(10)- and alpha-helix. The amide I' bands for all three peptides, under helix forming conditions, are between 1632 and 1635 cm-1. These results are incongruous with the assignment for alpha-helices in proteins where amide I' bands are usually found above 1650 cm-1. At elevated temperatures, all the peptides exhibit amide I' bands of 1642 cm-1, which is the accepted value for random coil. Variable temperature spectra for the 4K peptide (n = 4, X = Lys+), which is the most alpha-helical of the three peptides at 1 degree C, reveal an isosbestic point suggesting a cooperative two-state unfolding transition. The other peptides, however, did not reveal an isosbestic point, thereby indicating the presence of an intermediate, perhaps 3(10)-helix, along the thermal unfolding pathway.