CX3CL1

Fractalkine also known as chemokine (C-X3-C motif) ligand 1 is a is_associated_with::protein that in humans is encoded by the CX3CL1 is_associated_with::gene.

Function
Fractalkine is a large is_associated_with::cytokine protein of 373 amino acids, it contains multiple domains and is the only known member of the CX3C is_associated_with::chemokine family. It is also commonly known under the names fractalkine (in humans) and neurotactin (in mice). The polypeptide structure of CXC3L1 differs from the typical structure of other chemokines. For example, the spacing of the characteristic N-terminal is_associated_with::cysteines differs; there are three is_associated_with::amino acids separating the initial pair of cysteines in CX3CL1, with none in CC chemokines and only one intervening amino acid in CXC chemokines. CX3CL1 is produced as a long protein (with 373-amino acid in humans) with an extended is_associated_with::mucin-like stalk and a chemokine domain on top. The mucin-like stalk permits it to bind to the surface of certain cells. However a soluble (90 kD) version of this chemokine has also been observed. Soluble CX3CL1 potently chemoattracts is_associated_with::T cells and is_associated_with::monocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells, where it is primarily expressed. CX3CL1 elicits its adhesive and migratory functions by interacting with the chemokine receptor is_associated_with::CX3CR1. Its gene is located on human is_associated_with::chromosome 16 along with some CC chemokines known as is_associated_with::CCL17 and is_associated_with::CCL22.

CX3CL1 is up-regulated in the is_associated_with::hippocampus during a brief temporal window following is_associated_with::spatial learning, the purpose of which may be to regulate glutamate-mediated neurotransmission tone. This indicates a possible role for the chemokine in the protective plasticity process of is_associated_with::synaptic scaling.