Expression of secreted insulin-like growth factor-1 in Escherichia coli

The synthesis, processing and secretion of insulin-like growth factor-1 (IGF-1 or somatomedin-C) fused to LamB and OmpF secretion leader sequences in Escherichia coli have been investigated. Expression and secretion of IGF-1 was achieved. The major portion of this secreted IGF-1 accumulated in the periplasmic space as insoluble aggregates. A small amount of IGF-1 was found folded in its native conformation in the medium. The lamB and ompF signal sequences were fused to the 5' coding sequence of IGF-1. Fusion of the lamB signal sequence directly to IGF-1 (lamB-IGF-1) resulted in accumulation of 16-20 micrograms/A550/ml of correctly processed IGF-1 in the periplasmic space. The processing efficiency of LamB-IGF-1 and OmpF-IGF-1 was enhanced in an E. coli strain bearing a prlA4 mutation. Amino acid sequence analysis of IGF-1 secreted into the periplasm and exported into the medium confirmed the precise removal of the LamB or OmpF signal sequence. IGF-1 synthesized in E. coli was demonstrated to be active in a cell proliferation bioassay.