Sun Yi, Pumroy Ruth A, Mallik Leena, Chaudhuri Apala, Wang Chloe, Hwang Daniel, Danon Julia N, Dasteh Goli Kimia, Moiseenkova-Bell Vera Y, Sgourakis Nikolaos G
Department of Biochemistry and Biophysics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104.
Center for Computational and Genomic Medicine and Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2416992122. doi: 10.1073/pnas.2416992122. Epub 2025 Jan 9.
Class I major histocompatibility complex (MHC-I) proteins play a pivotal role in adaptive immunity by displaying epitopic peptides to CD8+ T cells. The chaperones tapasin and TAPBPR promote the selection of immunogenic antigens from a large pool of intracellular peptides. Interactions of chaperoned MHC-I molecules with incoming peptides are transient in nature, and as a result, the precise antigen proofreading mechanism remains elusive. Here, we leverage a high-fidelity TAPBPR variant and conformationally stabilized MHC-I, to determine the solution structure of the human antigen editing complex bound to a peptide decoy by cryogenic electron microscopy (cryo-EM) at an average resolution of 3.0 Å. Antigen proofreading is mediated by transient interactions formed between the nascent peptide binding groove with the P2/P3 peptide anchors, where conserved MHC-I residues stabilize incoming peptides through backbone-focused contacts. Finally, using our high-fidelity chaperone, we demonstrate robust peptide exchange on the cell surface across multiple clinically relevant human MHC-I allomorphs. Our work has important ramifications for understanding the selection of immunogenic epitopes for T cell screening and vaccine design applications.
I类主要组织相容性复合体（MHC-I）蛋白通过向CD8+ T细胞呈递表位肽在适应性免疫中起关键作用。分子伴侣塔帕辛（tapasin）和TAPBPR促进从大量细胞内肽中选择免疫原性抗原。分子伴侣辅助的MHC-I分子与进入的肽之间的相互作用本质上是短暂的，因此，精确的抗原校对机制仍然难以捉摸。在这里，我们利用一种高保真TAPBPR变体和构象稳定的MHC-I，通过低温电子显微镜（cryo-EM）以3.0 Å的平均分辨率确定与肽诱饵结合的人类抗原编辑复合物的溶液结构。抗原校对是由新生肽结合槽与P2/P3肽锚之间形成的短暂相互作用介导的，其中保守的MHC-I残基通过以主链为重点的接触稳定进入的肽。最后，使用我们的高保真分子伴侣，我们证明了在多个临床相关的人类MHC-I同种异型的细胞表面上存在强大的肽交换。我们的工作对于理解用于T细胞筛选和疫苗设计应用的免疫原性表位的选择具有重要意义。
