Schoel B, Zügel U, Ruppert T, Kaufmann S H
Department of Immunology, University of Ulm, FRG.
Eur J Immunol. 1994 Dec;24(12):3161-9. doi: 10.1002/eji.1830241237.
The peptides recognized by an H-2Db-restricted CD8 cytotoxic T lymphocyte (CTL) clone which is specific for the 60-kDa mycobacterial heat shock protein (hsp) and cross-reacts with stressed host cells were characterized. None of the nonapeptides from hsp60 conforming to the H-2Db binding motif were able to sensitize target cells for lysis by this CTL clone. Sequence analysis of the stimulatory fraction from a trypsin digest of hsp60, together with synthetic peptide studies, defined a cluster of overlapping epitopes. Carboxy-terminal extension by at least one amino acid of the nonamer predicted to bind best to H-2Db was essential for CTL recognition. Two such elongated peptides, a 10-mer and a 12-mer stimulated the clone at similarly low concentrations in the 100 pM range. We assume that these two peptides comply best with the natural epitope. In contrast, the 11-mer was inactive. The stimulatory 10-mer bound to H-2Db with an efficacy similar to that of the nonapeptide corresponding to the H-2Db motif, as revealed by peptide induced major histocompatibility complex (MHC) surface expression on RMA-S cells and competitive blocking of epitope recognition by the nonamer. Binding of these carboxy-terminally extended peptides to the MHC groove can be explained by anchoring through the amino acid residue Asn in position 5 of the peptide and by intrusion of the hydrophobic carboxy-terminal Ala (10-mer) or Leu (12-mer), but not Gly (11-mer), into the hydrophobic pocket of the H-2Db cleft. Because the carboxy-terminal part is thus larger than predicted, this region of the peptide may arch up from the binding groove. We assume that recognition of steric components of the MHC/peptide complex broaden the range of epitope specificity for a single T cell receptor. This flexibility not only promotes recognition of several overlapping peptides from a single antigen, but may also increase the chance of cross-reaction with similar peptides from unrelated proteins, including autoantigens. Consistent with this latter assumption, the T cell clone cross-recognizes mycobacterial hsp60 and stressed host cells.
对一种H-2Db限制性CD8细胞毒性T淋巴细胞（CTL）克隆所识别的肽段进行了表征，该克隆对60 kDa的分枝杆菌热休克蛋白（hsp）具有特异性，并与应激的宿主细胞发生交叉反应。符合H-2Db结合基序的hsp60非九肽均不能使靶细胞对该CTL克隆的裂解敏感。对hsp60胰蛋白酶消化产物的刺激部分进行序列分析，并结合合成肽研究，确定了一组重叠表位。预测与H-2Db结合最佳的九肽的羧基末端至少延伸一个氨基酸对于CTL识别至关重要。两种这样的延长肽，一种十肽和一种十二肽，在100 pM范围内以相似的低浓度刺激该克隆。我们假设这两种肽最符合天然表位。相比之下，十一肽无活性。肽诱导RMA-S细胞上主要组织相容性复合体（MHC）表面表达以及九肽对表位识别的竞争性阻断表明，具有刺激作用的十肽与对应于H-2Db基序的九肽以相似的效力结合H-2Db。这些羧基末端延伸肽与MHC凹槽的结合可以通过肽第5位氨基酸残基天冬酰胺的锚定以及疏水性羧基末端丙氨酸（十肽）或亮氨酸（十二肽）而非甘氨酸（十一肽）侵入H-2Db裂隙的疏水口袋来解释。由于羧基末端部分因此比预测的更大，肽的该区域可能从结合凹槽向上拱起。我们假设对MHC/肽复合物空间成分的识别拓宽了单个T细胞受体的表位特异性范围。这种灵活性不仅促进对来自单一抗原的几种重叠肽的识别，还可能增加与来自无关蛋白质（包括自身抗原）的相似肽发生交叉反应的机会。与后一种假设一致，该T细胞克隆交叉识别分枝杆菌hsp60和应激的宿主细胞。
