Quality Control of MHC Class I Restricted Antigen Processing

主要组织相容性复合体(MHC)I类糖蛋白是人类主要组织相容性复合体(MHC)的产物，是人类对病毒和细胞内病原体的T细胞介导的免疫反应的关键。它们是糖蛋白，与小分子β2-微球蛋白(？2M)形成异二聚体，并与来自细胞蛋白的多肽结合在细胞的内质网(ER)中。其中包括，当细胞 是受感染的、病原体编码的蛋白质。MHC I类分子与病原体来源的多肽形成的表面复合物可被CD8阳性的T细胞识别，从而杀死受感染的细胞。这项提议的目标是了解导致MHC I类复合体形成和细胞表面表达的详细分子过程，MHC I类复合体包含极高亲和力的多肽，这对CD8-T细胞反应至关重要，可以清除受感染的 病原体的个体。多肽与MHC I类分子的结合发生在称为多肽负载复合体或PLC的多蛋白质组装中。PLC由MHC I类分子本身、名为抗原处理相关转运蛋白(TAP)的异源二聚体转运体(将多肽输送到内质网)、Tapasin、膜糖蛋白和可溶性分子ERp57组成，后者可以介导I类分子之间的肽交换，最终生成高亲和力复合体，以及第二种名为calreticin的可溶性蛋白。负责PLC稳定性的相互作用涉及TAP和TAPASIN在膜内的特定结合，以及TAPASIN的管腔结构域与MHC I类分子之间的结合。ERp57和钙网蛋白之间也存在相互作用，以及内质网中其他折叠糖蛋白所共有的MHC I类糖蛋白与钙网蛋白的依赖于糖的相互作用。糖链结构通过两种相反的酶的作用来特征地动态维持，一种是葡萄糖苷酶II，它去除末端的葡萄糖残基，另一种是UDP-葡萄糖糖蛋白转移酶1(UGT1)，当含有该糖的糖蛋白被不适当地折叠时，它代替葡萄糖。这项提议试图确定这些不同的相互作用和酶机制在介导内质网中具有高亲和力的多肽的MHC I类分子组装中的作用。 公共卫生相关性：CD8阳性T细胞可清除感染者体内的病毒感染细胞，对有效的免疫反应至关重要。它们识别感染细胞表面的一个复合体，该复合体由来自病毒蛋白的多肽组成，在人类中，由感染细胞编码的人类白细胞抗原-A、B或C分子组成。这项建议试图详细了解对T细胞识别至关重要的人类白细胞抗原-多肽复合体是如何形成的。

DESCRIPTION (provided by applicant): Major Histocompatibility Complex (MHC) class I glycoproteins, the products of HLA-A, B and C genes in humans, are critical for T cell mediated immune responses to viruses and intracellular pathogens. They are glycoproteins that form a heterodimer with a small molecule, ?2-microglobulin (?2m), and associate in the endoplasmic reticulum (ER) of a cell with peptides derived from cellular proteins. These include, when the cell is infected, pathogen-encoded proteins. Surface complexes of MHC class I molecules with pathogen-derived peptides are recognized by CD8-positive T cells that can kill the infected cell. The goal of this proposal is to understand the detailed molecular processes that result in the formation and cell surface expression of MHC class I complexes that contain peptides of extraordinarily high affinity, which is essential for CD8-T cell responses that can rid an infected individual of the pathogen. Binding of peptides to MHC class I molecules occurs within a multi-protein assembly called the Peptide Loading Complex, or PLC. The PLC consists of MHC class I molecules themselves, a heterodimeric transporter called the Transporter associated with Antigen Processing (TAP) that delivers the peptides into the ER, tapasin, a membrane glycoprotein that, with a soluble molecule, ERp57, forms a disulfide-linked heterodimer that can mediate peptide exchange by the class I molecules to ultimately generate high affinity complexes, and a second soluble protein called calreticulin. The interactions responsible for the stability of the PLC involve specific associations of TAP and tapasin within the membrane, and between the luminal domains of tapasin and the MHC class I molecule. There are also interactions between ERp57 and calreticulin and a glycan-dependent interaction of the MHC class I glycoprotein with calreticulin that are shared by other folding glycoproteins in the ER. Th glycan structure is characteristically dynamically maintained by the action of two opposing enzymes, one, glucosidase II, that removes a terminal glucose residue, and a second, UDP-glucose glycoprotein transferase 1 (UGT1) that replaces the glucose when the glycoprotein bearing the glycan is improperly folded. This proposal seeks to determine the roles of these various interactions and enzymatic mechanisms in mediating the assembly of MHC class I molecules with high affinity peptides in the ER. PUBLIC HEALTH RELEVANCE: CD8-positive T cells eliminate virally infected cells from infected individuals and are critical for effective immune responses. They recognize a complex on the surface of an infected cell comprised of a peptide derived from a viral protein and, in humans, an HLA-A, B or C molecule encoded by the infected cell. This proposal seeks to understand in detail how the HLA-peptide complexes, critical for recognition by the T cells, are made.