Leggatt G R, Hosmalin A, Pendleton C D, Kumar A, Hoffman S, Berzofsky J A
Molecular Immunogenetics and Vaccine Research Section, Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1578, USA.
J Immunol. 1998 Nov 1;161(9):4728-35.
A minimal, nonamer epitope (TEMEKEGKI) from the reverse transcriptase protein of HIV-1, restricted by H-2Kk, was identified and the function of individual residues determined. Besides classical anchor residues at positions 2 and 9, methionine at position 3 was identified as an important MHC anchor and improved binding of a different (malarial) nonamer epitope to H-2Kk, albeit while also abolishing CTL recognition. Lysine at position 5 was replaceable by alanine for CTL raised against wild-type peptide but abolished recognition for CTL raised against the variant 5ALA peptide, indicating a unidirectional cross-reactivity. Interestingly, one CTL line raised against the 5ALA substituted peptide was permissive for a double substitution at positions 5 and 6, in which lysine was permissive at position 5 only if the adjacent glutamic acid was replaced by alanine. Extensive analysis revealed three distinct patterns of responses with peptides doubly substituted in this region: recognition of both single substitutions but not the double substitution, recognition of only one single substitution but also the double substitution, or recognition of both single substitutions and the double substitution. A second complementary substitution can therefore restore function lost through a first substitution. Thus, no residue acts independently of its neighbors, and pairs of substitutions may give results not predictable from the effects of each taken singly. This finding may have bearing on viral infections (such as HIV), in which the accumulation of two mutations in the epitope may lead to the reengagement of memory CTL previously silenced by the initial mutation.
鉴定出了来自HIV-1逆转录酶蛋白的一个最小的九聚体表位（TEMEKEGKI），其受H-2Kk限制，并确定了各个残基的功能。除了第2位和第9位的经典锚定残基外，第3位的甲硫氨酸被鉴定为一个重要的MHC锚定残基，它改善了另一个（疟疾的）九聚体表位与H-2Kk的结合，尽管同时也消除了CTL识别。对于针对野生型肽产生的CTL，第5位的赖氨酸可被丙氨酸替代，但对于针对变体5ALA肽产生的CTL则消除了识别，这表明存在单向交叉反应性。有趣的是，针对5ALA取代肽产生的一条CTL系允许在第5位和第6位进行双重取代，其中只有当相邻的谷氨酸被丙氨酸取代时，第5位的赖氨酸才是允许的。广泛分析揭示了该区域双重取代肽的三种不同反应模式：对两个单取代都有识别但对双重取代没有识别、只对一个单取代有识别但也对双重取代有识别、或者对两个单取代和双重取代都有识别。因此，第二个互补取代可以恢复因第一个取代而丧失的功能。这样，没有一个残基能独立于其相邻残基发挥作用，成对的取代可能会产生无法从单个取代的效果预测的结果。这一发现可能与病毒感染（如HIV）有关，在病毒感染中，表位中两个突变的积累可能导致先前因初始突变而沉默的记忆CTL重新激活。
