FGF-22

Fibroblast growth factor 22 (FGF22) is a 23 kDa, non-glycosylated member of the FGF7 subfamily, from the FGF family of heparin-binding growth factors. The human FGF22 precursor is 170 amino acids (aa) in length, and contains a 22 aa signal sequence with a 148 aa mature region (46) . The mature region shows a centrally-placed, 120 aa β-trefoil region (aa 43-168) that is characteristic of all FGF family members. Human FGF22 potentially has one alternate splice form. This isoform is 129 aa in length, and shows a 31 aa substitution for the first N-terminal 72 aa of the standard, or long, form. There is no information related to its possible function. Mature human FGF22 is 86% aa identical to mouse FGF22, with the mouse molecule showing a 9 aa deletion at the N-terminus. FGF 22 is synthesized by at least three cell types; keratinocytes, neurons, and skeletal muscle myotubes. In neurons and myotubes, FGF22 is presumed to function as an organizer of the presynaptic apparatus. Expressed by post-synaptic (or target) cells, FGF22 is believed to bind to FGF R2b on the surface of innervating processes, resulting in synaptic vesicle clustering, organization, and neurite branching. Although FGF22 is assumed to be secreted, little can be found in expressing cell culture media. Presumably, it is bound to 34 kDa FGFBP1, which is a molecule described as typically associated with cell membrane proteoglycans. Thus, following secretion, FGF22 could quickly be immobilized by FGFBP1, only to be released at a later time, or aided by FGFBP1 in its interaction with FGF R2b.