Characterization and crystallization of recombinant human neurotrophin-4

Neurotrophin-4 (NT-4) is the most recently discovered member of the neurotrophin family. We have expressed, refolded, and purified recombinant human NT-4 from Escherichia coli and compared it with recombinant human NT-4 secreted into the culture medium of baculovirus-infected insect cells. Both preparations were characterized and determined to be indistinguishable according to several biochemical criteria. Recombinant NT-4 from E. coli was crystallized in a form suitable for x-ray analysis, and characterization of these crystals indicated that NT-4 was present as a dimer within the asymmetric unit. NT-4 was active in promoting the survival of rat TrkB receptor-expressing fibroblasts, but was inactive on embryonic chicken sensory neurons, unlike the other members of the neurotrophin family and in contrast to the reported activities of partially purified NT-4.