<p>Heparin-binding growth factors I and II (HBGF) [<cite idref="PUB00000068"/>, <cite idref="PUB00005334"/>] (also known as acidic and basic fibroblast growth factors (FGF) are structurally related mitogens which stimulate growth or differentiation of a wide variety of cells of mesodermal or neuroectodermal origin. These two proteins belong to a family of growth factors and oncogenes which is a member of a superfamily that also contains the interleukin-1 proteins, Kunitz-type soybean trypsin inhibitors (STI) (see <db_xref db="INTERPRO" dbkey="IPR002160"/>) and histactophilin. All have very similar structures, but although the HBGF and interleukin-1 families share some sequence similarity (about 25% [<cite idref="PUB00000068"/>]), they show none at all to the STIs.</p><p>HBGFs are involved in many different processes related to cell differentiation and growth control [<cite idref="PUB00000068"/>]. HBGF1 and HBGF2 have similar effects: they induce mesoderm formation in embryogenesis, and mediate wound repair, angiogenesis and neural outgrowth; they also induce proliferation and migration of fibroblasts, endothelial cells and astroglial cells. HBGF3 (int-2) and HBGF4 (hst/ks) are known oncogenes, from stomach tumours and Kaposi sarcoma respectively. HBGF5 and HBGF6 are also oncogene products. HBGF7, keratinocyte growth factor, is possibly the major paracrine effector of normal epithelial cell proliferation.</p><p>These growth factors cause dimerisation of their tyrosine kinase receptors leading to intracellular signalling. There are currently four known tyrosine kinase receptors for fibroblast growth factors. These receptors can each bind several different members of this family [<cite idref="PUB00001036"/>].</p><p>The crystal structures of HBGF1 and HBGF2 [<cite idref="PUB00004736"/>] have been solved, showing them to have the same 12-stranded beta-sheet structure as both interleukin-1 and the Kunitz-type soybean trypsin inhibitors [<cite idref="PUB00003281"/>]; HBGF1 and interleukin-1 had been found to be similar, and they were predicted to have similar structures [<cite idref="PUB00005097"/>]. The beta-sheets are arranged in 3 similar lobes around a central axis, 6 strands forming an anti-parallel beta-barrel. Several regions of HBGF1 have been implicated in receptor binding, notably beta-strands 1-3, and the loop between strands 8 and 9. The loop between strands 10 and 11 is hought to be involved in binding heparin.</p> Heparin-binding growth factor/Fibroblast growth factor