FEATURES

FAMILY

DESCRIPTION

Also known as HLAE_HUMAN, HLA-E, HLA-6.2, HLAE. Non-classical major histocompatibility class Ib molecule involved in immune self-nonself discrimination. In complex with B2M/beta-2-microglobulin binds nonamer self-peptides derived from the signal sequence of classical MHC class Ia molecules (VL9 peptides) (PubMed:9754572, PubMed:18083576, PubMed:18339401). Peptide-bound HLA-E-B2M heterotrimeric complex primarily functions as a ligand for natural killer (NK) cell inhibitory receptor KLRD1-KLRC1, enabling NK cells to monitor the expression of other MHC class I molecules in healthy cells and to tolerate self (PubMed:9754572, PubMed:9486650, PubMed:17179229, PubMed:18083576). Upon cellular stress, preferentially binds signal sequence-derived peptides from stress-induced chaperones and is no longer recognized by NK cell inhibitory receptor KLRD1-KLRC1, resulting in impaired protection from NK cells (PubMed:12461076). Binds signal sequence-derived peptides from non-classical MHC class Ib HLA-G molecules and acts as a ligand for NK cell activating receptor KLRD1-KLRC2, likely playing a role in the generation and effector functions of adaptive NK cells and in maternal-fetal tolerance during pregnancy (PubMed:9754572, PubMed:30134159). Besides self-peptides, can also bind and present pathogen-derived peptides conformationally similar to VL9 peptides to alpha-beta T cell receptor (TCR) on unconventional CD8+ cytotoxic T cells, ultimately triggering antimicrobial immune response (PubMed:16474394, PubMed:30087334)., (Microbial infection) Viruses like human cytomegalovirus have evolved an escape mechanism whereby virus-induced down-regulation of host MHC class I molecules is coupled to the binding of viral peptides to HLA-E, restoring HLA-E expression and inducing HLA-E-dependent NK cell immune tolerance to infected cells., (Microbial infection) May bind HIV-1 gag/Capsid protein p24-derived peptide (AISPRTLNA) on infected cells and may inhibit NK cell cytotoxicity, a mechanism that allows HIV-1 to escape immune recognition., (Microbial infection) Upon SARS-CoV-2 infection, may contribute to functional exhaustion of cytotoxic NK cells and CD8-positive T cells (PubMed:32859121). Binds SARS-CoV-2 S/Spike protein S1-derived peptide (LQPRTFLL) expressed on the surface of lung epithelial cells, inducing NK cell exhaustion and dampening antiviral immune surveillance (PubMed:32859121). Forms a heterotrimer with B2M and a self- or a pathogen-derived peptide (peptide-bound HLA-E-B2M) (PubMed:18339401, PubMed:30087334). Similarly to MHC class Ia assembly, HLA-E-B2M heterodimer interacts with components of the antigen processing machinery TAPBP and TAP1-TAP2 complex; this interaction is required for peptide loading and translocation to the cell surface (PubMed:9427624). Interacts with CALCR; this interaction is required for appropriate folding (PubMed:9427624). The optimum binding peptide is a nonamer (VL9) that is primarily derived from amino-acid residues 3-11 of the signal sequences of most HLA-A, -B, -C and -G molecules (PubMed:9754572, PubMed:18083576, PubMed:9660937, PubMed:18339401). The VL9 peptide anchors to five main sites in the peptide-binding groove of HLA-E (PubMed:18339401). Peptide-bound HLA-E-B2M complex interacts with KLRD1-KLRC1 receptor on NK cells (PubMed:9486650, PubMed:18083576). Binds with lower affinity to activating KLRD1-KLRC2 (PubMed:18083576, PubMed:23335510). The common subunit KLRC1 plays a prominent role in directly interacting with HLA-E (PubMed:18083576). Peptide-bound HLA-E-B2M interacts with the alpha-beta TCR on unconventional CD8+ T cells (PubMed:16474394). Peptide-free HLA-E interacts with HLA-F-B2M complex; this interaction may regulate the intracellular trafficking and the stability of peptide-free MHC class I open conformers (OCs).

EXTERNAL LINKS

HLA-E

HLA class I histocompatibility antigen, alpha chain E

HLA-E

Molecular Synopsis