Vogt A B, Kropshofer H, Moldenhauer G, Hämmerling G J
Department of Molecular Immunology, German Cancer Research Center, Heidelberg, Germany.
Proc Natl Acad Sci U S A. 1996 Sep 3;93(18):9724-9. doi: 10.1073/pnas.93.18.9724.
The nonclassical major histocompatibility complex class II molecule HLA-DM (DM) has recently been shown to play a central role in the class II-associated antigen presentation pathway: DM releases invariant chain-derived CLIP peptides (class II-associated invariant chain protein peptide) from HLA-DR (DR) molecules and thereby facilitates loading with antigenic peptides. Some observations have led to the suggestion that DM acts in a catalytic manner, but so far direct proof is missing. Here, we investigated in vitro the kinetics of exchange of endogenously bound CLIP for various peptides on DR1 and DR2a molecules: we found that in the presence of DM the peptide loading process follows Michaelis-Menten kinetics with turnover numbers of 3-12 DR molecules per minute per DM molecule, and with KM values of 500-1000 nM. In addition, surface plasmon resonance measurements showed that DM interacts efficiently with DR-CLIP complexes but only weakly with DR-peptide complexes isolated from DM-positive cells. Taken together, our data provide evidence that DM functions as an enzyme-like catalyst of peptide exchange and favors the generation of long-lived DR-peptide complexes that are no longer substrates for DM.
非经典主要组织相容性复合体II类分子HLA-DM（DM）最近被证明在II类相关抗原呈递途径中起核心作用：DM从HLA-DR（DR）分子中释放恒定链衍生的CLIP肽（II类相关恒定链蛋白肽），从而促进抗原肽的加载。一些观察结果表明DM以催化方式起作用，但到目前为止还缺少直接证据。在这里，我们在体外研究了DR1和DR2a分子上内源性结合的CLIP与各种肽交换的动力学：我们发现，在DM存在的情况下，肽加载过程遵循米氏动力学，每个DM分子每分钟的转换数为3-12个DR分子，KM值为500-1000 nM。此外，表面等离子体共振测量表明，DM与DR-CLIP复合物有效相互作用，但与从DM阳性细胞中分离出的DR-肽复合物相互作用较弱。综上所述，我们的数据提供了证据，表明DM作为肽交换的类酶催化剂起作用，并有利于生成不再是DM底物的长寿DR-肽复合物。
