HLA-DQA1 - HLA class II histocompatibility antigen, DQ alpha 1 chain - human protein (Function)
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HLA-DQA1 »  HLA class II histocompatibility antigen, DQ alpha 1 chain
Protein also known as:  MHC class II DQA1.
Gene name:  HLA-DQA1
Family name: MHC class II
Entry whose protein(s) existence is based on evidence at protein level
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Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route, where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules, and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments, exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides, autophagosomes constitutively fuse with MHC class II loading compartments. In addition to APCs, other cells of the gastrointestinal tract, such as epithelial cells, express MHC class II molecules and CD74 and act as APCs, which is an unusual trait of the GI tract. To produce a MHC class II molecule that presents an antigen, three MHC class II molecules (heterodimers of an alpha and a beta chain) associate with a CD74 trimer in the ER to form a heterononamer. Soon after the entry of this complex into the endosomal/lysosomal system where antigen processing occurs, CD74 undergoes a sequential degradation by various proteases, including CTSS and CTSL, leaving a small fragment termed CLIP (class-II-associated invariant chain peptide). The removal of CLIP is facilitated by HLA-DM via direct binding to the alpha-beta-CLIP complex so that CLIP is released. HLA-DM stabilizes MHC class II molecules until primary high affinity antigenic peptides are bound. The MHC II molecule bound to a peptide is then transported to the cell membrane surface. In B-cells, the interaction between HLA-DM and MHC class II molecules is regulated by HLA-DO. Primary dendritic cells (DCs) also to express HLA-DO. Lysosomal microenvironment has been implicated in the regulation of antigen loading into MHC II molecules, increased acidification produces increased proteolysis and efficient peptide loading.  
  • UniProtKB
GO molecular function 
MHC class II receptor activitydefinition[GO:0032395]  
  • UniProtKB
Peptide antigen bindingdefinition[GO:0042605]  
  • UniProtKB
GO biological process 
Immune responsedefinition[GO:0006955]  
  • UniProtKB
According to KEGG, this protein belongs to the following pathways:
Allograft rejection  hsa05330+3117  
Antigen processing and presentation  hsa04612+3117  
Asthma  hsa05310+3117  
Autoimmune thyroid disease  hsa05320+3117  
Cell adhesion molecules (CAMs)  hsa04514+3117  
Graft-versus-host disease  hsa05332+3117  
Herpes simplex infection  hsa05168+3117  
HTLV-I infection  hsa05166+3117  
Influenza A  hsa05164+3117  
Intestinal immune network for IgA production  hsa04672+3117  
Leishmaniasis  hsa05140+3117  
Phagosome  hsa04145+3117  
Rheumatoid arthritis  hsa05323+3117  
Staphylococcus aureus infection  hsa05150+3117  
Systemic lupus erythematosus  hsa05322+3117  
Toxoplasmosis  hsa05145+3117  
Tuberculosis  hsa05152+3117  
Type I diabetes mellitus  hsa04940+3117  
Viral myocarditis  hsa05416+3117  
According to Reactome, this protein belongs to the following pathways:
Downstream TCR signaling  REACT_12555  
Generation of second messenger molecules  REACT_12623  
Interferon gamma signaling  REACT_25078  
MHC class II antigen presentation  REACT_121399  
PD-1 signaling  REACT_19324  
Phosphorylation of CD3 and TCR zeta chains  REACT_12582  
Translocation of ZAP-70 to Immunological synapse  REACT_12596  


Biological process 
Immunity  definition   [KW-0391]
Technical term 
Reference proteome  definition   [KW-1185]

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