Fu X T, Drover S, Marshall W H, Karr R W
Department of Immunology, G.D. Searle & Co., St. Louis, Missouri 63198, USA.
Hum Immunol. 1995 Aug;43(4):243-50. doi: 10.1016/0198-8859(95)00036-4.
Many residues involved in polymorphic antibody-binding epitopes on class II molecules are located on the alpha-helix of DR beta chains. Although they have received less attention, residues in the peptide-binding groove and second domain of the DR beta chain may also be critical for polymorphic anti-DR antibody epitopes. In this study, we used transfectants expressing site-directed mutations at positions in the HLA-DR beta 1 and beta 2 domains and flow cytometry to define the epitopes of several polymorphic anti-DR antibodies. Both DR(beta 10403) residues 14 and 25 were shown to be involved in the epitopes of mAbs DA6. 164, HU-20, Q5/6, and 50D6, and DR(beta 10701) residue 14 was shown to be critical for the epitopes of two DR7-specific mAbs, SFR 16-DR7M and TAL13.1. Unlike most other residues shown to be important in antibody-binding epitopes, residue 14 is located in the floor of the peptide-binding groove and residue 25 is in an outer loop, each with their side chains pointing down, such that antibodies may directly contact these residues from below the binding groove. Two residues in the beta 2 domain, beta 180 and beta 181, were also shown to be involved in the epitopes of three polymorphic anti-DR mAbs, NFLD.D1, NFLD.M1, and LY9. Although these two residues are close to the transmembrane domain in the linear sequence, their solvent accessibility in the DR1 structures is quite impressive. Our data provide new evidence that residues accessible under the peptide-binding groove contribute to polymorphic antibody-binding epitopes.
II类分子上多态性抗体结合表位所涉及的许多残基位于DRβ链的α螺旋上。尽管它们受到的关注较少，但DRβ链的肽结合槽和第二结构域中的残基对于多态性抗DR抗体表位可能也很关键。在本研究中，我们使用了在HLA-DRβ1和β2结构域中表达定点突变的转染子，并通过流式细胞术来确定几种多态性抗DR抗体的表位。结果显示，DR（β10403）的第14和25位残基参与了单克隆抗体DA6.164、HU-20、Q5/6和50D6的表位形成，DR（β10701）的第14位残基对于两种DR7特异性单克隆抗体SFR 16-DR7M和TAL13.1的表位至关重要。与大多数在抗体结合表位中显示重要性的其他残基不同，第14位残基位于肽结合槽的底部，第25位残基位于外环，它们的侧链都向下指，这样抗体可能从结合槽下方直接接触这些残基。β2结构域中的两个残基β180和β181也被证明参与了三种多态性抗DR单克隆抗体NFLD.D1、NFLD.M1和LY9的表位形成。尽管这两个残基在线性序列中靠近跨膜结构域，但它们在DR1结构中的溶剂可及性相当可观。我们的数据提供了新的证据，表明在肽结合槽下方可及的残基有助于多态性抗体结合表位的形成。
