Dynamic properties of MHC class II allotypes

主要组织相容性复合体（MHC）的蛋白质在整个人群中表达为数百种不同的等位基因变体（同种异型）。MHC基因座的这种多态性和蛋白质变体的相应表达的结果是个体的免疫肽是不同的，并且呈现致病性、自身免疫相关或肿瘤相关抗原的倾向也不同。为了理解想要的和不想要的免疫应答，因此了解肽选择的关键步骤是至关重要的。理解MHC II类分子的抗原呈递的中心是HLA-DM催化的占位符CLIP（II类相关不变链肽）与更高亲和力肽的交换。肽交换率的巨大差异的理解不能单独用静态晶体结构来解释，但需要一种方法，捕捉MHCII-肽复合物的基本动态特征。在这项提案中，我们的目标是（i）确定MHC-肽复合物，强烈不同的HLA-DM依赖性，（ii）调查这些MHCII同种异型的动态特性，通过NMR光谱和（iii）确定DM催化交换的酶促参数。这将使我们能够确定决定单个MHCII-肽复合物的HLA-DM易感性的关键氨基酸和分子中间体。在第二个，最初独立的项目的一部分，我们将描绘细胞的肽（iv）的MHCII肽复合物的第1部分和（v）的肿瘤细胞系。最后，将比较分子机制和细胞结果，以确定MHCII动力学对细胞抗原呈递的影响。

Proteins of the Major Histocompatibility Complex (MHC) are expressed as hundreds of different allelic variants (allotypes) across the human population. This polymorphic nature of the MHC gene locus and the corresponding expression of protein variants has the consequence that the immune peptidomes of individuals are distinct, and that the propensities to display pathogenic, autoimmune-related or tumor-associated antigens also differ. For the understanding of wanted and unwanted immune responses it is therefore essential to know the critical steps of peptide selection. Central for an understanding of antigen presentation by MHC class II molecules is the HLA-DM-catalyzed exchange of the placeholder CLIP (class II associated invariant chain peptide) against higher affine peptides. The understanding of the large differences in peptide exchange rates cannot be explained by static crystal structures alone, but requires an approach that captures the essential dynamic features of MHCII-peptide complexes. In this proposal we aim to (i) identify MHC-peptide complexes that strongly differ in their HLA-DM dependency, (ii) investigate the dynamic properties of these MHCII allotypes by NMR spectroscopy and to (iii) determine the enzymatic parameters of DM-catalyzed exchange. This will allow us to define the critical amino acids and molecular intermediates that determine HLA-DM susceptibility of individual MHCII-peptide complexes. In a second, initially independent part of the project we will delineate the cellular peptidomes of (iv) the MHCII peptide complexes investigated in Part 1 and (v) of tumor cell lines. Finally, the molecular mechanistic and cellular findings will be compared to define the impact of MHCII dynamics on cellular antigen presentation.