Zappacosta F, Tabaczewski P, Parker K C, Coligan J E, Stroynowski I
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
J Immunol. 2000 Feb 15;164(4):1906-15. doi: 10.4049/jimmunol.164.4.1906.
The biological properties of the nonclassical class I MHC molecules secreted into blood and tissue fluids are not currently understood. To address this issue, we studied the murine Q10 molecule, one of the most abundant, soluble class Ib molecules. Mass spectrometry analyses of hybrid Q10 polypeptides revealed that alpha1alpha2 domains of Q10 associate with 8-9 long peptides similar to the classical class I MHC ligands. Several of the sequenced peptides matched intracellularly synthesized murine proteins. This finding and the observation that the Q10 hybrid assembly is TAP2-dependent supports the notion that Q10 groove is loaded by the classical class I Ag presentation pathway. Peptides eluted from Q10 displayed a binding motif typical of H-2K, D, and L ligands. They carried conserved residues at P2 (Gly), P6 (Leu), and Pomega (Phe/Leu). The role of these residues as anchors/auxiliary anchors was confirmed by Ala substitution experiments. The Q10 peptide repertoire was heterogeneous, with 75% of the groove occupied by a multitude of diverse peptides; however, 25% of the molecules bound a single peptide identical to a region of a TCR V beta-chain. Since this peptide did not display enhanced binding affinity for Q10 nor does its origin and sequence suggest that it is functionally significant, we propose that the nonclassical class I groove of Q10 resembles H-2K, D, and L grooves more than the highly specialized clefts of nonclassical class I Ags such as Qa-1, HLA-E, and M3.
目前尚不清楚分泌到血液和组织液中的非经典I类MHC分子的生物学特性。为了解决这个问题，我们研究了小鼠Q10分子，它是最丰富的可溶性Ib类分子之一。对杂交Q10多肽的质谱分析表明，Q10的α1α2结构域与8-9个长肽结合，类似于经典I类MHC配体。一些测序的肽与细胞内合成的小鼠蛋白匹配。这一发现以及Q10杂交组装依赖TAP2的观察结果支持了Q10凹槽由经典I类抗原呈递途径加载的观点。从Q10洗脱的肽显示出H-2K、D和L配体典型的结合基序。它们在P2（甘氨酸）、P6（亮氨酸）和Pω（苯丙氨酸/亮氨酸）处带有保守残基。丙氨酸替代实验证实了这些残基作为锚定/辅助锚定的作用。Q10肽库是异质的，75%的凹槽被多种不同的肽占据；然而，25%的分子结合了一种与TCR Vβ链区域相同的单一肽。由于这种肽对Q10没有显示出增强的结合亲和力，其来源和序列也没有表明它具有功能意义，我们提出Q10的非经典I类凹槽更类似于H-2K、D和L凹槽，而不是非经典I类抗原如Qa-1、HLA-E和M3的高度特化裂隙。
