Improved preparation and crystallization of 25 kDa human fibroblast growth factor-9

We prepared 25 kDa human fibroblast growth factor‐9 (hFGF‐9 N33) on a large scale after overproduction in Escherichia coli MM294 (DE3)/pTG931. The purification was performed by a combination of hydrophobic chromatography and HPLC with an ion exchange column, a heparin affinity column and a gel filtration column. This improved procedure was rapid and simple, and the purified hFGF‐9 N33 was found to be homogeneous as judged by various criteria, such as amino acid analysis, N‐terminal amino acid sequence, C‐terminal amino acid analysis and biological activity. Furthermore, as determined by low endotoxin and DNA content, the protein was of high purity. In addition, the hFGF‐9 N33 prepared in the present study was easily crystallized by the vapour diffusion method.