Recombinant Human FGF-22 Protein

Fibroblast growth factor-22 (FGF-22) is a 23 kDa, non-glycosylated member of the FGF-7 subfamily, from the FGF family of heparin-binding growth factors (1-3). The human FGF-22 precursor is 170 amino acids (aa) in length, and contains a 22 aa signal sequence with a 148 aa mature region (4-6). The mature region shows a centrally-placed, 120 aa beta-trefoil region (aa 43-168) that is characteristic of all FGF family members. Human FGF-22 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 (7). There is no information related to its possible function. Mature human FGF-22 is 86% aa identical to mouse FGF-22, with the mouse molecule showing a 9 aa deletion at the N-terminus (5). FGF-22 is synthesized by at least three cell types; keratinocytes, neurons, and skeletal muscle myotubes (4, 8, 9). In neurons and myotubes, FGF-22 is presumed to function as an organizer of the presynaptic apparatus. Expressed by postsynaptic (or target) cells, FGF-22 is believed to bind to FGF R2b on the surface of innervating processes, resulting in synaptic vesicle clustering, organization, and neurite branching (8, 10). Although FGF-22 is assumed to be secreted, little can be found in expressing cell culture media. Presumably, it is bound to 34 kDa FGF-BP1, which is a molecule described as typically associated with cell membrane proteoglycans (6, 11). Thus, following secretion, FGF-22 could quickly be immobilized by FGF-BP1, only to be released at a later time, or aided by FGF-BP1 in its interaction with FGF R2b (6, 10, 11).