CXC chemokine receptor type 4, member of the class A family of seven-transmembrane G protein-coupled receptors
CXCR4 is the only known G protein-coupled chemokine receptor for the key homeostatic ligand CXCL12, which is constitutively secreted by bone marrow stromal cells. Atypical chemokine receptor CXCR7 (ACKR3) also binds CXCL12, but activates signaling in a G protein-independent manner. CXCR4 is also a co-receptor for HIV infection and plays critical roles in the development of immune system during both lymphopoiesis and myelopoiesis. Chemokines are principal regulators for leukocyte trafficking, recruitment, and activation. Chemokine family membership is defined on the basis of sequence homology and on the presence of variations on a conserved cysteine motif, which allows the family to further divide into four subfamilies (CC, CXC, XC, and CX3C). Chemokines interact with seven-transmembrane receptors which are typically coupled to G protein for signaling. Currently, there are ten known receptors for CC chemokines, seven for CXC chemokines, and single receptors for the XC and CX3C chemokines.
Comment:Small-molecule chemical ligands tend to bind deeper within the receptor core, compared to a peptide ligand neurotensin, which binds towards the extracellular surface of its receptor.
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