Department of Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA.
Transplant Immunology Laboratory, Department of Surgery, Albany Medical College, Albany, New York, USA.
J Biol Chem. 2023 Jul;299(7):104869. doi: 10.1016/j.jbc.2023.104869. Epub 2023 May 27.
MHC class II molecules function to present exogenous antigen-derived peptides to CD4 T cells to both drive T cell activation and to provide signals back into the class II antigen-presenting cell. Previous work established the presence of multiple GxxxG dimerization motifs within the transmembrane domains of MHC class II α and β chains across a wide range of species and revealed a role for differential GxxxG motif pairing in the formation of two discrete mouse class II conformers with distinct functional properties (i.e., M1-and M2-paired I-A class II). Biochemical and mutagenesis studies detailed herein extend this model to human class II by identifying an anti-HLA-DR mAb (Tü36) that selectively binds M1-paired HLA-DR molecules. Analysis of the HLA-DR allele reactivity of the Tü36 mAb helped define other HLA-DR residues involved in mAb binding. In silico modeling of both TM domain interactions and whole protein structure is consistent with the outcome of biochemical/mutagenesis studies and provides insight into the possible structural differences between the two HLA-DR conformers. Cholesterol depletion studies indicate a role for cholesterol-rich membrane domains in the formation/maintenance of Tü36 mAb reactive DR molecules. Finally, phylogenetic analysis of the amino acid sequences of Tü36-reactive HLA-DR β chains reveals a unique pattern of both Tü36 mAb reactivity and key amino acid polymorphisms. In total, these studies bring the paradigm M1/M2-paired MHC class II molecules to the human HLA-DR molecule and suggest that the functional differences between these conformers defined in mouse class II extend to the human immune system.
MHC II 类分子的功能是将外源性抗原衍生肽呈递给 CD4 T 细胞，从而既能驱动 T 细胞激活，又能向 II 类抗原呈递细胞提供信号。先前的工作已经在广泛的物种中证实了 MHC II 类 α 和 β 链跨膜结构域中存在多个 GxxxG 二聚化基序，并揭示了不同 GxxxG 基序配对在形成两种具有不同功能特性的离散鼠类 II 类构象体中的作用（即 M1-和 M2-配对的 I-A 类 II 类）。本文详细的生化和突变研究将该模型扩展到人类 II 类，鉴定了一种抗 HLA-DR mAb（Tü36），该 mAb 特异性结合 M1-配对的 HLA-DR 分子。对 Tü36 mAb 对 HLA-DR 等位基因反应性的分析有助于确定其他涉及 mAb 结合的 HLA-DR 残基。TM 结构域相互作用和整个蛋白质结构的计算机建模与生化/突变研究的结果一致，并为理解两种 HLA-DR 构象体之间可能的结构差异提供了线索。胆固醇耗竭研究表明富含胆固醇的膜结构域在 Tü36 mAb 反应性 DR 分子的形成/维持中起作用。最后，对 Tü36 反应性 HLA-DRβ链的氨基酸序列进行系统发育分析揭示了 Tü36 mAb 反应性和关键氨基酸多态性的独特模式。总的来说，这些研究将 M1/M2-配对的 MHC II 类分子的范例扩展到人类 HLA-DR 分子，并表明在鼠类 II 类中定义的这些构象体之间的功能差异扩展到人类免疫系统。
