UniProt functional annotation for P01730

UniProt code: P01730.

Organism: Homo sapiens (Human).
Taxonomy: Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; Catarrhini; Hominidae; Homo.
Function: Accessory protein for MHC class-II antigen/T-cell receptor interaction. May regulate T-cell activation. Induces the aggregation of lipid rafts.
Subunit: Associates with LCK. Binds to HIV-1 gp120 and to P4HB/PDI and upon HIV-1 binding to the cell membrane, is part of P4HB/PDI- CD4-CXCR4-gp120 complex. Interacts with HIV-1 Envelope polyprotein gp160 and protein Vpu. Interacts with Human Herpes virus 7 capsid proteins. Interacts with PTK2/FAK1; this interaction requires the presence of HIV-1 gp120.
Subcellular location: Cell membrane; Single-pass type I membrane protein. Note=Localizes to lipid rafts. Removed from plasma membrane by HIV-1 Nef protein that increases clathrin-dependent endocytosis of this antigen to target it to lysosomal degradation. Cell surface expression is also down-modulated by HIV-1 Envelope polyprotein gp160 that interacts with, and sequesters CD4 in the endoplasmic reticulum.
Ptm: Palmitoylation and association with LCK contribute to the enrichment of CD4 in lipid rafts.
Polymorphism: The OKT monoclonal antibodies are widely used for the analysis of human peripheral blood T-lymphocytes. OKT4 reacts with T-helper/inducer lymphocytes. The OKT4 epitope of the CD4 cell-surface protein is polymorphic in white, black, and Japanese populations. The variable phenotypic expression is due a CD4 polymorphism. OKT4 positive individuals carry Arg-265 and OKT4 negative individuals carry Trp-265 [MIM:613949].
Miscellaneous: Primary receptor for HIV-1.
Similarity: Contains 3 Ig-like C2-type (immunoglobulin-like) domains.
Similarity: Contains 1 Ig-like V-type (immunoglobulin-like) domain.

Annotations taken from UniProtKB at the EBI.