Kinase Family GASK
The GASK (Golgi-Associated Kinase) kinases are a recently-emerging family of atypical PKL-fold kinases which function in the Golgi to phosphorylate secreted proteins and sugar residues on glycoproteins and are sometimes secreted. The founding member, Drosophila four-jointed phosphorylates a cadherin substrate on the extracellular domain and is implicated in planar cell polarity. FAM20B can phosphorylate xylose sugars within proteoglycans, and both FAM20A, FAM20B and FAM20C are associated with abnormalities in bone and tooth mineralization in humans and zebrafish. Some FK proteins may also be secreted from the cell.
GASK kinases lack the R of the HRD motif and have no conserved phosphorylable residues in their short predicted activation loops, suggesting that they are not controlled by autophosphorylation. These proteins are generally not seen to be phosphorylated (http://phosphosite.org)
The GASK family has the following subfamilies: