A Viral, Transporter Associated with Antigen Processing (TAP)-independent, High Affinity Ligand with Alternative Interactions Endogenously Presented by the Nonclassical Human Leukocyte Antigen E Class I Molecule

Elena Lorente,Susana Infantes,David Abia,Eilon Barnea,Ilan Beer,Ruth García,Fátima Lasala,Mercedes Jiménez,Carmen Mir,Antonio Morreale,Arie Admon,Daniel López

doi:10.1074/jbc.m112.362293

Abstract

The transporter associated with antigen processing (TAP) enables the flow of viral peptides generated in the cytosol by the proteasome and other proteases to the endoplasmic reticulum, where they complex with nascent human leukocyte antigen (HLA) class I. Later, these peptide-HLA class I complexes can be recognized by CD8(+) lymphocytes. Cancerous cells and infected cells in which TAP is blocked, as well as individuals with unusable TAP complexes, are able to present peptides on HLA class I by generating them through TAP-independent processing pathways. Here, we identify a physiologically processed HLA-E ligand derived from the D8L protein in TAP-deficient vaccinia virus-infected cells. This natural high affinity HLA-E class I ligand uses alternative interactions to the anchor motifs previously described to be presented on nonclassical HLA class I molecules. This octameric peptide was also presented on HLA-Cw1 with similar binding affinity on both classical and nonclassical class I molecules. In addition, this viral peptide inhibits HLA-E-mediated cytolysis by natural killer cells. Comparison between the amino acid sequences of the presenting HLA-E and HLA-Cw1 alleles revealed a shared structural motif in both HLA class molecules, which could be related to their observed similar cross-reactivity affinities. This motif consists of several residues located on the floor of the peptide-binding site. These data expand the role of HLA-E as an antigen-presenting molecule.

Highlights

Individuals with nonfunctional transporter associated with antigen processing (TAP) present ligands generated by TAP-independent processing pathways associated with classical human leukocyte antigen (HLA) class I molecules
The transporter associated with antigen processing (TAP) enables the flow of viral peptides generated in the cytosol by the proteasome and other proteases to the endoplasmic reticulum, where they complex with nascent human leukocyte antigen (HLA) class I
The results reported here show that the 112–119 octamer derived from the vaccinia D8L protein is efficiently presented by the MHC class I molecule HLA-E using alternative interactions with the anchor motifs previously described for this nonclassical MHC class I molecule

Summary

Background

Individuals with nonfunctional transporter associated with antigen processing (TAP) present ligands generated by TAP-independent processing pathways associated with classical HLA class I molecules. We identify a physiologically processed HLA-E ligand derived from the D8L protein in TAP-deficient vaccinia virus-infected cells This natural high affinity HLA-E class I ligand uses alternative interactions to the anchor motifs previously described to be presented on nonclassical HLA class I molecules. OCTOBER 12, 2012 VOLUME 287 NUMBER 42 of viral proteins by the proteasome and other cytosolic proteases [1] This degradation generates short peptides of 8 –11 amino acids, which are translocated to the endoplasmic reticulum lumen by transporter associated with antigen processing (TAP), where they assemble with newly synthesized HLA class I heavy chain and ␤2-microglobulin. HLA-E is a nonclassical class I molecule that binds monomorphic signal peptides derived from classical HLA class I proteins This complex is the ligand of innate receptors expressed mainly by natural killer cells and thereby regulates lymphocyte activity [13]. We explore a possible role for HLA-E in presenting some of the previously described TAP-independent VACV ligands

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION