The T lymphocyte response to cytochrome c. V. Determination of the minimal peptide size required for stimulation of T cell clones and assessment of the contribution of each residue beyond this size to antigenic potency.
The T lymphocyte response to cytochrome c. V. Determination of the minimal peptide size required for stimulation of T cell clones and assessment of the contribution of each residue beyond this size to antigenic potency.
复制标题
T淋巴细胞对细胞色素c的反应。
作者：
R. Schwartz;B. Fox;E. Fraga;C. Chen;B. Singh
B10.A T细胞对鸽子细胞色素c的增殖反应主要针对位于分子羧基末端的单个抗原决定簇。在本实验中，我们使用合成的肽类似物的羧基末端序列的蛾细胞色素c，探索抗原效力的结构要求。能够刺激完全反应的最小尺寸肽随T细胞克隆而变化，但在所研究的生物系统的限制内，显示为蛾片段97-103。在氨基末端添加更多的氨基酸以不均匀的增量增加了抗原效力，其中在残基95处做出了很大的贡献。在这个位置的氨基酸取代的分析提供了没有证据表明，它包含一个残基，直接接触T细胞受体。相反，与利用螺旋-卷曲转变理论的分析的良好一致性表明，该残基以及其他残基通过有助于α-螺旋构型中分子二级结构的稳定来增加抗原效力。链长对抗原效力的最大影响似乎在残基93处停止，与理论分析一致。然而，在残基93上再添加几个氨基末端残基显示出一个额外的显著增加，即效力增加。这几乎完全是由位于第93位残基谷氨酸之外四个氨基酸处的单个赖氨酸（大约一圈α-螺旋）造成的。为了实验性地测试α-螺旋形成趋势是否可以解释较大类似物的增加的效力，通过圆二色性测量来评估三氟乙醇中螺旋形成的程度。对于链长从蛾95-103增加到蛾86-90; 94-103的肽，发现抗原效力和α-螺旋百分比之间存在良好的相关性。这些结果表明，二级结构可能在决定参与T淋巴细胞活化的抗原决定簇的效力中起重要作用。
The B10.A T cell proliferative response to pigeon cytochrome c is mainly directed against a single antigenic determinant located at the carboxy-terminal end of the molecule. In the present experiments, we used synthetic peptide analogs of the carboxy-terminal sequence of moth cytochrome c to explore the structural requirements for antigenic potency. The minimum-sized peptide capable of stimulating a full response varied with the T cell clone, but within the limits of the biological systems studied, was shown to be moth fragment 97-103. Addition of more amino acids at the amino terminal end increased the antigenic potency in uneven increments, with a large contribution being made at residue 95. Analysis of amino acid substitutions at this position provided no evidence that it contained a residue that directly contacted the T cell receptor. Instead, good agreement with an analysis that made use of helix-coil transition theory suggested that this residue, as well as others, increased antigenic potency by contributing to the stabilization of the secondary structure of the molecule in an alpha-helical configuration. The maximum effect of chain length on antigenic potency appeared to stop at residue 93, in agreement with the theoretical analysis. However, addition of several more amino-terminal residues to residue 93 showed one additional significant increment of increased potency. This was almost entirely accounted for by a single lysine located four amino acids beyond the glutamic acid at residue 93 (approximately one turn of an alpha-helix away). To experimentally test whether alpha-helix-forming tendencies could account for the increased potency of the larger analogs, the degree of helix formation in trifluoroethanol was assessed by circular dichroism measurements. A good correlation was found between antigenic potency and percentage of alpha-helix for peptides of increasing chain length from moth 95-103 up to moth 86-90; 94-103. These results suggest that secondary structure may play an important role in determining the potency of antigenic determinants involved in the activation of T lymphocytes.