Crystal structure of the N-myristoylated lipopeptide-bound MHC class I complex.

Daisuke Morita,Tatsuhiko Igarashi,Yoshimasa Tanaka,Masahiko Sugita,Juri Suzuki,Kazuhiro Iwai,Yukie Yamamoto,Takashi Shiina,Hiroaki Fujita,Naoki Mori,Hidetoshi Inoko,Bunzo Mikami,Takeshi Ishikawa,Tatsuaki Mizutani

doi:10.1038/ncomms10356

Abstract

The covalent conjugation of a 14-carbon saturated fatty acid (myristic acid) to the amino-terminal glycine residue is critical for some viral proteins to function. This protein lipidation modification, termed N-myristoylation, is targeted by host cytotoxic T lymphocytes (CTLs) that specifically recognize N-myristoylated short peptides; however, the molecular mechanisms underlying lipopeptide antigen (Ag) presentation remain elusive. Here we show that a primate major histocompatibility complex (MHC) class I-encoded protein is capable of binding N-myristoylated 5-mer peptides and presenting them to specific CTLs. A high-resolution X-ray crystallographic analysis of the MHC class I:lipopeptide complex reveals an Ag-binding groove that is elaborately constructed to bind N-myristoylated short peptides rather than prototypic 9-mer peptides. The identification of lipopeptide-specific, MHC class I-restricted CTLs indicates that the widely accepted concept of MHC class I-mediated presentation of long peptides to CTLs may need some modifications to incorporate a novel MHC class I function of lipopeptide Ag presentation.

Highlights

The covalent conjugation of a 14-carbon saturated fatty acid to the amino-terminal glycine residue is critical for some viral proteins to function
As b2m-associated major histocompatibility complex (MHC) class I molecules may restrict the recognition of C14nef[5] by 2N5.1, we isolated an array of rhesus MHC (Mamu) class I complementary DNA clones from a donor with the potential to present C14nef[5] to 2N5.1 and transfected each cDNA clone into the monkey kidney epithelial cell line LLC-MK2
Key findings obtained by pioneering studies, including the milestone discovery of the X-ray crystallographic structure of the ligand-bound HLA-A2 molecule, have established that MHC class I molecules bind 8- to 10-mer peptides and present them to specific CTLs18,19

Summary

Introduction

The covalent conjugation of a 14-carbon saturated fatty acid (myristic acid) to the amino-terminal glycine residue is critical for some viral proteins to function This protein lipidation modification, termed N-myristoylation, is targeted by host cytotoxic T lymphocytes (CTLs) that recognize N-myristoylated short peptides; the molecular mechanisms underlying lipopeptide antigen (Ag) presentation remain elusive. N-myristoylated Nef peptide-specific T cells were found to expand significantly in the peripheral blood of SIV-infected monkeys and the plasma viral load in the infected monkeys correlated reciprocally with the number of circulating lipopeptide-specific T cells These findings suggest that besides peptides (presented by MHC class I) and lipids (presented by group 1 CD1), lipopeptides may comprise a novel chemical class of Ags targeted by CTLs with implications in the host defense against viral infection; the identity of the lipopeptide Ag-presenting molecules currently remains unknown. These results suggest that MHC class I molecules may have evolved to include those binding N-myristoylated short peptides, thereby assisting CTLs to sense the N-myristoylation of viral proteins

Methods

Results

Conclusion