HLA class II histocompatibility antigen, DR alpha chain is a protein that in humans is encoded by the HLA-DRA gene.[1] HLA-DRA encodes the alpha subunit of HLA-DR. Unlike the alpha chains of other Human MHC class II molecules, the alpha subunit is practically invariable. However it can pair with, in any individual, the beta chain from 3 different DR beta loci, DRB1, and two of any DRB3, DRB4, or DRB5 alleles. Thus there is the potential that any given individual can form 4 different HLA-DR isoforms (2 alleles of DRB1 and two alleles from DRB3, DRB4 or DRB5).
The polypeptidesubunit encoded by this gene belongs to the HLA class II alpha chain paralogues. The class II protein is a heterodimer consisting of an alpha (DRα) and a beta chain (DRβ), both anchored in the membrane. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. Class II molecules are expressed in antigen presenting cells (APC: B lymphocytes, dendritic cells, macrophages).[1]
Gene structure and polymorphisms
The alpha chain is approximately 33-35 kDa and its gene contains 5 exons. Exon 1 encodes the leader peptide, exons 2 and 3 encode the two extracellular domains, and exon 4 encodes the transmembrane domain and the cytoplasmic tail. DRA does not have polymorphisms in the peptide binding part and acts as the sole alpha chain for DRB1, DRB3, DRB4 and DRB5.[1]
Alleles
There are two different HLA-DRA chains in the human population coded by three different DRA alleles:
Bénichou S, Benmerah A (2003). "[The HIV nef and the Kaposi-sarcoma-associated virus K3/K5 proteins: "parasites"of the endocytosis pathway]". Med Sci (Paris). 19 (1): 100–6. doi:10.1051/medsci/2003191100. PMID12836198.
Tolstrup M, Ostergaard L, Laursen AL, et al. (2004). "HIV/SIV escape from immune surveillance: focus on Nef". Curr. HIV Res. 2 (2): 141–51. doi:10.2174/1570162043484924. PMID15078178.
Anderson JL, Hope TJ (2005). "HIV accessory proteins and surviving the host cell". Current HIV/AIDS Reports. 1 (1): 47–53. doi:10.1007/s11904-004-0007-x. PMID16091223.
Li L, Li HS, Pauza CD, et al. (2006). "Roles of HIV-1 auxiliary proteins in viral pathogenesis and host-pathogen interactions". Cell Res. 15 (11–12): 923–34. doi:10.1038/sj.cr.7290370. PMID16354571.
Piatier-Tonneau D, Gastinel LN, Amblard F, et al. (1991). "Interaction of CD4 with HLA class II antigens and HIV gp120". Immunogenetics. 34 (2): 121–8. doi:10.1007/BF00211424. PMID1869305.
Nong Y, Kandil O, Tobin EH, et al. (1991). "The HIV core protein p24 inhibits interferon-gamma-induced increase of HLA-DR and cytochrome b heavy chain mRNA levels in the human monocyte-like cell line THP1". Cell. Immunol. 132 (1): 10–6. doi:10.1016/0008-8749(91)90002-S. PMID1905983.
Rosenstein Y, Burakoff SJ, Herrmann SH (1990). "HIV-gp120 can block CD4-class II MHC-mediated adhesion". J. Immunol. 144 (2): 526–31. PMID1967269.
Callahan KM, Fort MM, Obah EA, et al. (1990). "Genetic variability in HIV-1 gp120 affects interactions with HLA molecules and T cell receptor". J. Immunol. 144 (9): 3341–6. PMID1970352.
Koppelman B, Cresswell P (1990). "Rapid nonlysosomal degradation of assembled HLA class II glycoproteins incorporating a mutant DR alpha-chain". J. Immunol. 145 (8): 2730–6. PMID2212658.
Clayton LK, Sieh M, Pious DA, Reinherz EL (1989). "Identification of human CD4 residues affecting class II MHC versus HIV-1 gp120 binding". Nature. 339 (6225): 548–51. doi:10.1038/339548a0. PMID2543930.
Diamond DC, Sleckman BP, Gregory T, et al. (1988). "Inhibition of CD4+ T cell function by the HIV envelope protein, gp120". J. Immunol. 141 (11): 3715–7. PMID2846691.
Tjernlund U, Scheynius A, Johansson C, et al. (1989). "T-cell response to purified protein derivative after removal of Langerhans' cells from epidermal cell suspensions containing keratinocytes expressing class II transplantation antigens". Scand. J. Immunol. 28 (6): 667–73. doi:10.1111/j.1365-3083.1988.tb01500.x. PMID3266023.
Andrieu JM, Even P, Venet A (1986). "AIDS and related syndromes as a viral-induced autoimmune disease of the immune system: an anti-MHC II disorder. Therapeutic implications". AIDS research. 2 (3): 163–74. doi:10.1089/aid.1.1986.2.163. PMID3489470.
1pyw: Human class II MHC protein HLA-DR1 bound to a designed peptide related to influenza virus hemagglutinin, FVKQNA(MAA)AL, in complex with staphylococcal enterotoxin C3 variant 3B2 (SEC3-3B2)
2ipk: Crystal Structure of the MHC Class II Molecule HLA-DR1 in Complex with the Fluorogenic Peptide, AcPKXVKQNTLKLAT (X=3-[5-(dimethylamino)-1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl]-L-alanine) and the Superantigen, SEC3 Variant 3B2