THEORETICAL-STUDY OF THE CONTRIBUTION OF AROMATIC SIDE-CHAINS TO THE CIRCULAR-DICHROISM OF BASIC BOVINE PANCREATIC TRYPSIN-INHIBITOR
THEORETICAL-STUDY OF THE CONTRIBUTION OF AROMATIC SIDE-CHAINS TO THE CIRCULAR-DICHROISM OF BASIC BOVINE PANCREATIC TRYPSIN-INHIBITOR
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DOI：
10.1021/bi00447a051
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发表时间：
1989-10-17
期刊：
影响因子：
2.9
通讯作者：
WOODY, RW
中科院分区：
文献类型：
--
作者：
MANNING, MC;WOODY, RW
圆二色性（CD）光谱经常用于确定蛋白质的二级结构组成。然而，这假设用于这些分析的光谱的远UV区域仅归因于多肽主链的贡献。碱性牛胰蛋白酶抑制剂（BPTI）具有不寻常的远紫外CD光谱，这使得这样的分析困难。这种差异的一个可能原因是其他发色团，如芳香族侧链（四个酪氨酸，四个苯丙氨酸），可能是负责的。通过采用矩阵方法的变化计算了BPTI的CD光谱。仅包括肽主链给出了理论与实验之间的差的一致性。这被认为与所进行的计算的质量无关。随后包括酪氨酸的贡献并没有改善拟合。然而，进一步包括苯丙氨酸发色团提供了一个很好的拟合之间的计算和实验远紫外光谱。重要的贡献来自由两个酪氨酸（Tyr 21和Tyr 23）和三个苯丙氨酸（Phe 22，Phe 4和Phe 45）形成的芳香族氨基酸簇。考虑两种类型的侧链和整个肽骨架是产生CD曲线的准确描述所必需的。总体而言，这些结果表明，芳香族氨基酸的贡献可以显着干扰蛋白质的远紫外CD光谱，使二级结构分析困难。这在如BPTI的系统中尤其如此，具有低量的α-螺旋结构和芳香族氨基酸簇。
Circular dichroism (CD) spectroscopy is frequently employed to determine the secondary structure composition of a protein. However, this assumes that the far-UV region of the spectrum, which is used for these analyses, is due only to contributions from the polypeptide backbone. Basic bovine pancreatic trypsin inhibitor (BPTI) possesses an unusual far-UV CD spectrum, which has made such an analysis difficult. One possible reason for the discrepancy is that other chromophores, such as the aromatic side chains (four tyrosines, four phenylalanines), might be responsible. The CD spectrum of BPTI was calculated by employing a variation of the matrix method. Including only the peptide backbone gave poor agreement between theory and experiment. This was sown to be independent of the quality of the calculation performed. Subsequent inclusion of tyrosine contributions did little to improve the fit. However, further inclusion of the phenylalanine chromophores provided a good fit between the calculated and experimental far-UV spectrum. The important contributions arise from the cluster of aromatic amino acids formed by two tyrosines (Tyr21 and Tyr23) and three phenylalanines (Phe22, Phe4, and Phe45). Consideration of both types of side chains and the entire peptide backbone is essential to produce an accurate description of the CD curve. Overall, these results indicate that contributions from aromatic amino acids can significantly perturb the far-UV CD spectrum of a protein, making secondary structure analysis difficult. This is particularly true in systems like BPTI, with low amounts of .alpha.-helical structure and clusters of aromatic amino acids.