Kraft J R, Vance R E, Pohl J, Martin A M, Raulet D H, Jensen P E
Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
J Exp Med. 2000 Sep 4;192(5):613-24. doi: 10.1084/jem.192.5.613.
The major histocompatibility complex class Ib protein, Qa-1(b), serves as a ligand for murine CD94/NKG2A natural killer (NK) cell inhibitory receptors. The Qa-1(b) peptide-binding site is predominantly occupied by a single nonameric peptide, Qa-1 determinant modifier (Qdm), derived from the leader sequence of H-2D and L molecules. Five anchor residues were identified in this study by measuring the peptide-binding affinities of substituted Qdm peptides in experiments with purified recombinant Qa-1(b). A candidate peptide-binding motif was determined by sequence analysis of peptides eluted from Qa-1 that had been folded in the presence of random peptide libraries or pools of Qdm derivatives randomized at specific anchor positions. The results indicate that Qa-1(b) can bind a diverse repertoire of peptides but that Qdm has an optimal primary structure for binding Qa-1(b). Flow cytometry experiments with Qa-1(b) tetramers and NK target cell lysis assays demonstrated that CD94/NKG2A discriminates between Qa-1(b) complexes containing peptides with substitutions at nonanchor positions P4, P5, or P8. Our findings suggest that it may be difficult for viruses to generate decoy peptides that mimic Qdm and raise the possibility that competitive replacement of Qdm with other peptides may provide a novel mechanism for activation of NK cells.
主要组织相容性复合体 Ib 类蛋白 Qa-1(b) 作为小鼠 CD94/NKG2A 自然杀伤（NK）细胞抑制性受体的配体。Qa-1(b) 肽结合位点主要被源自 H-2D 和 L 分子前导序列的单一九聚体肽 Qa-1 决定簇修饰物（Qdm）占据。在本研究中，通过在纯化的重组 Qa-1(b) 实验中测量取代的 Qdm 肽的肽结合亲和力，确定了五个锚定残基。通过对从在随机肽库或在特定锚定位置随机化的 Qdm 衍生物库存在下折叠的 Qa-1 洗脱的肽进行序列分析，确定了一个候选肽结合基序。结果表明，Qa-1(b) 可以结合多种肽，但 Qdm 具有结合 Qa-1(b) 的最佳一级结构。用 Qa-1(b) 四聚体进行的流式细胞术实验和 NK 靶细胞裂解试验表明，CD94/NKG2A 能够区分在非锚定位置 P4、P5 或 P8 有取代的肽的 Qa-1(b) 复合物。我们的研究结果表明，病毒可能难以产生模仿 Qdm 的诱饵肽，并增加了用其他肽竞争性取代 Qdm 可能提供激活 NK 细胞新机制的可能性。
