CD4 antigen

1CDH, 1CDI, 1CDJ, 1CDU, 1CDY, 1G9M, 1G9N, 1GC1, 1JL4, 1Q68, 1RZJ, 1RZK, 1WIO, 1WIP, 1WIQ, 2B4C, 2JKR, 2JKT, 2KLU, 2NXY, 2NXZ, 2NY0, 2NY1, 2NY2, 2NY3, 2NY4, 2NY5, 2NY6, 2QAD, 3B71, 3CD4, 3JWD, 3JWO, 3LQA, 3O2D, 3S5L, 3T0E, 4JM2, 1WBR, 3S4S, 4H8W, 4P9H, 4Q6I, 4R2G, 4R4H, 4RQS, 3J70, 5A7X, 5A8H, 5CAY92012504ENSG00000010610ENSMUSG00000023274P01730P06332NM_000616NM_001195014NM_001195015NM_001195016NM_001195017NM_013488NP_000607NP_001181943NP_001181944NP_001181945NP_001181946NP_038516In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 (after the OKT4 monoclonal antibody that reacted with it) before being named CD4 in 1984. In humans, the CD4 protein is encoded by the CD4 gene.1cdh: STRUCTURES OF AN HIV AND MHC BINDING FRAGMENT FROM HUMAN CD4 AS REFINED IN TWO CRYSTAL LATTICES1cdi: STRUCTURES OF AN HIV AND MHC BINDING FRAGMENT FROM HUMAN CD4 AS REFINED IN TWO CRYSTAL LATTICES1cdj: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD41cdu: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD4 MUTANT WITH PHE 43 REPLACED BY VAL1cdy: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD4 MUTANT WITH GLY 47 REPLACED BY SER1g9m: HIV-1 HXBC2 GP120 ENVELOPE GLYCOPROTEIN COMPLEXED WITH CD4 AND INDUCED NEUTRALIZING ANTIBODY 17B1g9n: HIV-1 YU2 GP120 ENVELOPE GLYCOPROTEIN COMPLEXED WITH CD4 AND INDUCED NEUTRALIZING ANTIBODY 17B1gc1: HIV-1 GP120 CORE COMPLEXED WITH CD4 AND A NEUTRALIZING HUMAN ANTIBODY1jl4: CRYSTAL STRUCTURE OF THE HUMAN CD4 N-TERMINAL TWO DOMAIN FRAGMENT COMPLEXED TO A CLASS II MHC MOLECULE1q68: Solution structure of T-cell surface glycoprotein CD4 and Proto-oncogene tyrosine-protein kinase LCK fragments1rzj: HIV-1 HXBC2 GP120 ENVELOPE GLYCOPROTEIN COMPLEXED WITH CD4 AND INDUCED NEUTRALIZING ANTIBODY 17B1rzk: HIV-1 YU2 GP120 ENVELOPE GLYCOPROTEIN COMPLEXED WITH CD4 AND INDUCED NEUTRALIZING ANTIBODY 17B1wio: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD4, TETRAGONAL CRYSTAL FORM1wip: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD4, MONOCLINIC CRYSTAL FORM1wiq: STRUCTURE OF T-CELL SURFACE GLYCOPROTEIN CD4, TRIGONAL CRYSTAL FORM2b4c: Crystal structure of HIV-1 JR-FL gp120 core protein containing the third variable region (V3) complexed with CD4 and the X5 antibody2nxy: HIV-1 gp120 Envelope Glycoprotein(S334A) Complexed with CD4 and Antibody 17b2nxz: HIV-1 gp120 Envelope Glycoprotein (T257S, S334A, S375W) Complexed with CD4 and Antibody 17b2ny0: HIV-1 gp120 Envelope Glycoprotein (M95W, W96C, T257S, V275C, S334A, S375W, A433M) Complexed with CD4 and Antibody 17b2ny1: HIV-1 gp120 Envelope Glycoprotein (I109C, T257S, S334A, S375W, Q428C) Complexed with CD4 and Antibody 17b2ny2: HIV-1 gp120 Envelope Glycoprotein (T123C, T257S, S334A, S375W, G431C) Complexed with CD4 and Antibody 17b2ny3: HIV-1 gp120 Envelope Glycoprotein (K231C, T257S, E267C, S334A, S375W) Complexed with CD4 and Antibody 17b2ny4: HIV-1 gp120 Envelope Glycoprotein (K231C, T257S, E268C, S334A, S375W) Complexed with CD4 and Antibody 17b2ny5: HIV-1 gp120 Envelope Glycoprotein (M95W, W96C, I109C, T257S, V275C, S334A, S375W, Q428C, A433M) Complexed with CD4 and Antibody 17b2ny6: HIV-1 gp120 Envelope Glycoprotein (M95W, W96C, I109C, T123C, T257S, V275C,S334A, S375W, Q428C, G431C) Complexed with CD4 and Antibody 17b3cd4: REFINEMENT AND ANALYSIS OF THE FIRST TWO DOMAINS OF HUMAN CD4 In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 (after the OKT4 monoclonal antibody that reacted with it) before being named CD4 in 1984. In humans, the CD4 protein is encoded by the CD4 gene. CD4+ T helper cells are white blood cells that are an essential part of the human immune system. They are often referred to as CD4 cells, T-helper cells or T4 cells. They are called helper cells because one of their main roles is to send signals to other types of immune cells, including CD8 killer cells, which then destroy the infectious particle. If CD4 cells become depleted, for example in untreated HIV infection, or following immune suppression prior to a transplant, the body is left vulnerable to a wide range of infections that it would otherwise have been able to fight. Like many cell surface receptors/markers, CD4 is a member of the immunoglobulin superfamily. It has four immunoglobulin domains (D1 to D4) that are exposed on the extracellular surface of the cell: The immunoglobulin variable (IgV) domain of D1 adopts an immunoglobulin-like β-sandwich fold with seven β-strands in 2 β-sheets, in a Greek key topology. CD4 interacts with the β2-domain of MHC class II molecules through its D1 domain. T cells displaying CD4 molecules (and not CD8) on their surface, therefore, are specific for antigens presented by MHC II and not by MHC class I (they are MHC class II-restricted). MHC class I contains Beta-2 microglobulin. The short cytoplasmic/intracellular tail (C) of CD4 contains a special sequence of amino acids that allow it to recruit and interact with the tyrosine kinase Lck. CD4 is a co-receptor of the T cell receptor (TCR) and assists the latter in communicating with antigen-presenting cells. The TCR complex and CD4 each bind to distinct regions of the antigen-presenting MHCII molecule - α1/β1 and β2, respectively. In CD4 the interaction involves its extracellular D1 domain. The resulting close proximity between the TCR complex and CD4 (extracellular and intracellular) allows the tyrosine kinase Lck bound to the cytoplasmic tail of CD4 to tyrosine-phosphorylate the Immunoreceptor tyrosine activation motifs (ITAM) on the cytoplasmic domains of CD3 to amplify the signal generated by the TCR. Lck is essential for the activation of many molecular components of the signaling cascade of an activated T cell. Depending on the signal, different types of T helper cells result. Phosphorylated ITAM motifs on CD3 recruit and activate SH2 domain-containing protein tyrosine kinases (PTK) such as Zap70 to further mediate downstream signalling through tyrosine phosphorylation, leading to transcription factor activation including NF-κB and consequent T cell activation. CD4 has also been shown to interact with SPG21, Lck and Protein unc-119 homolog.