Molecular basis for presentation of N-myristoylated peptides by the chicken YF1∗7.1 molecule.

Major histocompatibility complex I (MHC-I) and MHC-I-like molecules play a central role in mediating immunity. Through their conservation across all taxa of jawed vertebrates, the MHC-I-like proteins have adapted to present non-peptidic antigens to distinct T cell populations. While our understanding of the structure-function relationship of MHC-I and MHC-I-like molecules in humans and mice is well established, the nature of the antigens presented by MHC-I- like molecules in "non-model" species remains unclear. Here, using a mammalian recombinant expression system combined with mass spectrometry approaches, we identified N-myristoylated peptides as endogenous ligands for the chicken MHC-I-like protein YF1∗7.1. Given the importance of N-myristoylation in viral pathogenesis, we determined the crystal structure of YF1∗7.1 in complex with two N-myristoylated peptides derived from Marek's disease virus (MDV), demonstrating the molecular basis that underpins the presentation of N-myristoylated peptides from MDV, a highly contagious and fatal viral neoplastic disease in chickens. Thus, the identified ligands are distinct from unmodified peptides found in classical MHC-I and -II as well as diverse amphipathic lipids captured by CD1 proteins. Collectively, our study lays the foundation for further molecular and functional characterization of YF1∗7.1 and more broadly of the role of the MHC-I encoded by the MHC-Y gene cluster in protection against highly contagious viral neoplastic diseases in chickens.