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.