Sette A, Lamont A, Buus S, Colon S M, Miles C, Grey H M
Cytel, La Jolla, CA 92037.
J Immunol. 1989 Aug 15;143(4):1268-73.
In an attempt to define some of the conformational requirements for binding of the antigenic peptide OVA 323-336 to purified IAd molecules, three distinct experimental approaches were applied. First, the effect of introducing proline or glycine residues within the region of OVA 323-336 crucial for its IAd binding capacity was analyzed. In most instances these substitutions had little or no effect, suggesting that neither alpha-helical nor beta-sheet regular structures may be strictly required for productive interaction with MHC molecules. Some of the same substitutions were also found to have no effect on the capacity of the peptide to stimulate OVA 323-336 specific T cell hybridomas, suggesting that regular structures such as alpha-helices or beta-sheets may not be strictly required for T cell stimulation, either. Second, we introduced, within the OVA 323-336 molecule, structural modifications predicted to alter its dipole characteristics and stabilize helical structures. No improvement of the IAd binding capacity was detected following these structural alterations. Surprisingly, some but not others of these analogs displayed increased antigenicity for OVA 323-336 specific T cell hybridomas. Third, a panel of analogs of OVA 323-336 were synthesized in which the crucial IAd binding core region was linked to non-native sequences of differing conformational propensities. When 22 such analogs were tested for IAd binding, it was found that these non-native sequences could drastically influence the binding capacity, but no correlation was found between their effect and their alpha-helical, beta-sheet, or beta-turn conformational propensity as calculated by the Chou and Fasman algorithm. In summary, all the data presented herein suggest that, at least in the case of OVA 323-336 and IAd, the propensity of the antigen molecule to form secondary structures such as alpha-helices, beta-sheets, or beta-turns does not correlate with its capacity to bind MHC molecules.
为了确定抗原肽OVA 323 - 336与纯化的IAd分子结合的一些构象要求，我们采用了三种不同的实验方法。首先，分析了在OVA 323 - 336中对其IAd结合能力至关重要的区域引入脯氨酸或甘氨酸残基的影响。在大多数情况下，这些取代几乎没有影响，这表明与MHC分子进行有效相互作用可能并不严格要求α-螺旋或β-折叠等规则结构。还发现其中一些相同的取代对该肽刺激OVA 323 - 336特异性T细胞杂交瘤的能力也没有影响，这表明α-螺旋或β-折叠等规则结构对于T细胞刺激可能也不是严格必需的。其次，我们在OVA 323 - 336分子中引入了预计会改变其偶极特性并稳定螺旋结构的结构修饰。在这些结构改变后，未检测到IAd结合能力的提高。令人惊讶的是，这些类似物中的一些（但不是其他类似物）对OVA 323 - 336特异性T细胞杂交瘤显示出增强的抗原性。第三，合成了一组OVA 323 - 336的类似物，其中关键的IAd结合核心区域与具有不同构象倾向的非天然序列相连。当测试22种此类类似物的IAd结合时，发现这些非天然序列可极大地影响结合能力，但未发现它们的影响与其通过Chou和Fasman算法计算的α-螺旋、β-折叠或β-转角构象倾向之间存在相关性。总之，本文给出的所有数据表明，至少在OVA 323 - 336和IAd的情况下，抗原分子形成α-螺旋、β-折叠或β-转角等二级结构的倾向与其结合MHC分子的能力无关。
