PEPTIDE BINDING AND EXPRESSION OF MHC CLASS I MOLECULES

目前对少校抗原呈递的普遍看法 组织相容性复合体(MHC)I类分子是这些分子 结合来自外源蛋白或自身蛋白的结合多肽 呈现细胞。然后将这些多肽与MHC结合起来呈现 抗原特异性的I类分子，MHC I类分子限制性T细胞 CD8+细胞毒性T淋巴细胞(CTL)的细胞受体；这种相互作用 最终应导致提呈细胞或靶细胞的细胞溶解 CTL.MHC-I类分子的结晶学分析揭示了一种凹槽 建议将多肽结合并呈现在其中；此外， 这些研究表明MHC I类分子的沟槽中可能存在残基。 可以与抗原肽相互作用的分子。进行的研究 作者：Townsen等人。已经暗示抗原肽在 I类分子的折叠和组装；此外，这些研究 这表明这一过程导致了从内质网到细胞表面的出口。 然而，Ploegh和他的同事最近的研究产生了一个 关于这一机制的争论(S)(及其生理意义) 通过这个过程可以发生，因为他们能够证明I类 分子能够在细胞表面由多肽诱导组装。我们 之前已经证明了小鼠I类分子Ld是 运输到细胞表面的速度更慢，与Beta2-m的关联更少 与大多数其他MHC第I类相比，表面表达较低 分子；Hansen和他的同事发现LD的表面表达 在细胞与LD限制性抗原孵育后，可增加 多肽。最近，我们鉴定了一种识别改变形式的单抗 可能代表Ldalt的未组装前体。因此，Ld 是研究抗原提呈作用的理想模型系统 在MHC I类分子的表面表达中。第一个目标是 建议确定LD的哪些氨基酸残基是 通过分析LD样蛋白的表达来确定其表达表型 分子，并通过创造和研究嵌合体和 突变的LD分子。第二，为了解决上述争议，我们建议 评估上述ldalt和beta2-m在大会中的作用 过程，并检测体内多肽诱导的动力学 进程。第三，我们建议分析LD、类LD和 含抗原肽和取代肽的突变LD分子 几种不同的分析方法，包括体外多肽结合分析。 这些分析应该确定哪些LD残基与多肽有关 具有约束力，并应导致更好地理解“地形”的 多肽与I类分子的相互作用。总体上，完成 这些研究应该有助于阐明抗原肽所起的作用 在第I类的表面表达和随后的抗原呈递中 以及涉及到的I类分子上的残基 这些过程。

The current consensus view of antigen presentation by major histocompatibility complex (MHC) class I molecules is that these molecules bind peptides derived from foreign or self-proteins synthesized within the presenting cell. The peptides are then presented in association with MHC class I molecules to antigen-specific, MHC class I molecule-restricted T cell receptor on CD8+ cytotoxic T lymphocytes (CTL); this interaction ultimately should result in cytolysis of the presenting or target cell by CTL. Crystallographic analyses of MHC class I molecules revealed a groove into which peptides are proposed to be bound and presented; furthermore, these studies suggested potential residues in the groove of MHC class I molecules that could interact with antigenic peptides. Studies performed by Townsend et al. have implicated a role for antigenic peptide in the folding and assembly of class I molecules; furthermore, these studies suggested that this process led to egress from the ER to the cell surface. However, recent studies by Ploegh and coworkers have generated a controversy concerning the mechanism(s) (and its physiological relevance) by which that process can occur, since they were able to show that class I molecules are capable of peptide-induced assembly at the cell surface. We have previously demonstrated that the murine class I molecule, Ld, is transported to the cell surface more slowly, associates with beta2-m less strongly and displays lower surface expression than most other MHC class I molecules; Hansen and colleagues showed that the surface expression of Ld could be increased upon incubation of cells with Ld-restricted antigenic peptides. Recently, we characterized a mAb that recognizes an altered form of Ldalt that may represent an unassembled precursor of Ld. Thus, Ld represents an ideal model system to study the role of antigen presentation in surface expression of MHC class I molecules. The first objective of the proposal is to determine which amino acid residues of Ld are responsible for its expression phenotype by analyzing the expression of Ld-like molecules, and by creating and studying the expression of chimeric and mutant Ld molecules. Second, to resolve the above controversy, we propose to assess the role of aforementioned Ldalt and beta2-m in the assembly process, and to examine the kinetics if the in vivo peptide-induction process. Third, we propose to analyze the interaction of Ld, Ld-like, and mutant Ld molecules with antigenic peptides and substituted peptides in several different assays including an in vitro peptide binding assay. These analyses should determine which Ld residues are involved in peptide binding and should lead to be a better understanding of the "topography" of the peptide-class I molecule interaction. Collectively, completion of these studies should help elucidate the role that antigenic peptides play in surface expression of and subsequent antigen presentation by class I molecules and as well as the residues on class I molecules involved in these processes.