Kinase Subfamily FJ
FJ kinases are Golgi-associated kinases that phosphorylated secreted and surface proteins and have a role in cadherin signaling. They are remote members of the PKL kinase fold and members of the GASK (Golgi-Associated Kinase) family.
Like other FJ family kinases, FJ has a conserved signal peptide but no predicted transmembrane domain. The PKL-type kinase domain is at the C-terminus, with a variable (~200? AA) N-terminus with no known domain and lower sequence conservation than the kinase domain.
FJ is single copy in all vertebrates (FJX1) and is generally single copy in other deuterostomes and arthropods, but has not been seen elsewhere.
Drosophila four-jointed was shown to phosphorylate cadherin proteins within the Golgi apparatus, specifically the cadherin domains of the planar polarity (PCP) genes Fat and Daschous .
Mouse FJX1 inhibits dendrite extension in the hippocampus . Mouse knockouts have abnormal hippocampus morphology and cultured hippocampal neurons show increased dendrite branching and extension. Addition of FJX1 protein to hippocampal cultures had the opposite effect, suggesting that FJX1 may act extracellularly.
- Ishikawa HO, Takeuchi H, Haltiwanger RS, and Irvine KD. Four-jointed is a Golgi kinase that phosphorylates a subset of cadherin domains. Science. 2008 Jul 18;321(5887):401-4. DOI:10.1126/science.1158159 |
- Probst B, Rock R, Gessler M, Vortkamp A, and Püschel AW. The rodent Four-jointed ortholog Fjx1 regulates dendrite extension. Dev Biol. 2007 Dec 1;312(1):461-70. DOI:10.1016/j.ydbio.2007.09.054 |