Structure of the human class I histocompatibility antigen, HLA-A2

The class I histocompatibility antigen from human cell membranes has two structural motifs: the membrane-proximal end of the glycoprotein contains two domains with immunoglobulin-folds that are paired in a novel manner, and the region distal from the membrane is a platform of eight antiparallel β-strands topped by α-helices. A large groove between the α-helices provides a binding site for processed foreign antigens. An unknown 'antigen' is found in this site in crystals of purified HLA-A2. © 1987 Nature Publishing Group.