Crystal structure of HLA-A2 bound to LIR-1, a host and viral major histocompatibility complex receptor

Leukocyte immunoglobulin-like receptor 1 (LIR-1), an inhibitory receptor expressed on monocytes, dendritic cells and lymphocytes, regulates cellular function by binding a broad range of classical and nonclassical major histocompatibility complex (MHC) class I molecules, and the human cytomegalovirus MHC class I homolog UL18. Here we describe the 3.4-Å crystal structure of a complex between the LIR-1 D1D2 domains and the MHC class I molecule HLA-A2. LIR-1 contacts the mostly conserved β_2-microglobulin and 3 domains of HLA-A2. The LIR-1 binding site comprises residues at the interdomain hinge, and a patch at the D1 tip. The structure shows how LIR-1 recognizes UL18 and diverse MHC class I molecules, and indicates that a similar mode of MHC class I recognition is used by other LIR family members.