cd00271: Chemokine_C (This model is not part of the current CDD release)
C motif chemokine subfamily
Chemokines (or chemotactic cytokines) are small secreted growth factors and interferons that signal through their G-protein coupled chemokine receptors. They are divided into 4 subfamilies based on the arrangement of the two N-terminal cysteines: CXC, CC, C or (X)C, and CX3C. This model represents the C or (X)C subfamily. There are two human paralogous proteins belonging to this subfamily, XC chemokine ligand 1 (XCL1) and XC chemokine ligand 2 (XCL2). XCL1 is also called C motif chemokine 1, lymphotactin, lymphotaxin, cytokine SCM-1 or small-inducible cytokine C1. It differs structurally to other chemokines since it contains only one of the two disulfide bridges that are conserved in other members of the family. It also contains a unique C-terminal extension, which is required for biological activity and is thought to play a role in receptor binding. XCL1 interconverts between two distinct structures with distinct functions. One XCL1 fold resembles the structure of all other chemokines (chemokine fold), while the other does not (alternate fold). The chemokine fold of XCL1 displays high affinity for its receptor XCR1, a typical seven-transmembrane G-protein-coupled receptor (GPCRR), while the alternative fold binds GAGs and exhibits antimicrobial activity. XCL1, a mediator of mucosal immunity, has been found to chemoattract neutrophils and B cells through the XCR1 and is thought to be a factor in acute allograft rejection and inflammatory bowel disease. XCL2, also called C motif chemokine 2 or cytokine SCM-1 beta, shares a receptor with XCL1 and is expected to be structurally similar. It has been characterized as a cancer prognosis and immune infiltration-related biomarker.
Jiyao W et al.(2023). "The conserved domain database in 2023.",