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Chemokine (C-X3-C motif) ligand 1
Protein CX3CL1 PDB 1b2t.png
PDB rendering based on 1b2t.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols CX3CL1 ; ABCD-3; C3Xkine; CXC3; CXC3C; NTN; NTT; SCYD1; fractalkine; neurotactin
External IDs OMIM601880 MGI1097153 HomoloGene2251 GeneCards: CX3CL1 Gene
RNA expression pattern
PBB GE CX3CL1 823 at tn.png
PBB GE CX3CL1 203687 at tn.png
More reference expression data
Species Human Mouse
Entrez 6376 20312
Ensembl ENSG00000006210 ENSMUSG00000031778
UniProt P78423 O35188
RefSeq (mRNA) NM_002996 NM_009142
RefSeq (protein) NP_002987 NP_033168
Location (UCSC) Chr 16:
57.41 – 57.42 Mb
Chr 8:
94.77 – 94.78 Mb
PubMed search [1] [2]

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


Fractalkine is a large cytokine protein of 373 amino acids, it contains multiple domains and is the only known member of the CX3C chemokine family. It is also commonly known under the names fractalkine (in humans) and neurotactin (in mice).[1][2] The polypeptide structure of CXC3L1 differs from the typical structure of other chemokines. For example, the spacing of the characteristic N-terminal cysteines differs; there are three 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 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 T cells and monocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells, where it is primarily expressed.[2] CX3CL1 elicits its adhesive and migratory functions by interacting with the chemokine receptor CX3CR1.[3] Its gene is located on human chromosome 16 along with some CC chemokines known as CCL17 and CCL22.[2][4]

CX3CL1 is up-regulated in the hippocampus during a brief temporal window following 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 synaptic scaling.[5]


  1. ^ Pan Y, Lloyd C, Zhou H, Dolich S, Deeds J, Gonzalo JA et al. (1997). "Neurotactin, a membrane-anchored chemokine upregulated in brain inflammation". Nature 387 (6633): 611–617. doi:10.1038/42491. PMID 9177350. 
  2. ^ a b c Bazan JF, Bacon KB, Hardiman G, Wang W, Soo K, Rossi D et al. (1997). "A new class of membrane-bound chemokine with a CX3C motif". Nature 385 (6617): 640–644. doi:10.1038/385640a0. PMID 9024663. 
  3. ^ Imai T, Hieshima K, Haskell C, Baba M, Nagira M, Nishimura M et al. (1997). "Identification and molecular characterization of fractalkine receptor CX3CR1, which mediates both leukocyte migration and adhesion". Cell 91 (4): 521–530. doi:10.1016/S0092-8674(00)80438-9. PMID 9390561. 
  4. ^ Nomiyama H, Imai T, Kusuda J, Miura R, Callen DF, Yoshie O (1998). "Human chemokines fractalkine (SCYD1), MDC (SCYA22) and TARC (SCYA17) are clustered on chromosome 16q13". Cytogenet. Cell Genet 81 (1): 10–11. doi:10.1159/000015000. PMID 9691168. 
  5. ^ Sheridan GK, Wdowicz A, Pickering M, Watters O, Halley P, O'Sullivan NC et al. (2014). "CX3CL1 is up-regulated in the rat hippocampus during memory-associated synaptic plasticity". Front Cell Neurosci 8: 233. doi:10.3389/fncel.2014.00233. PMC 4130185. PMID 25161610. 

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