Expression, Purification, Characterization of Amphioxus Insulin-like Peptide and Preparation of Polyclonal Antibody to It.

To elucidate the origination and evolution as well as structure-function relationship of insulin and IGF-1, the gene of amphioxus insulin-like peptide (ILP), a common ancestor of insulin and IGF-1, was chemically synthesized and cloned into the expression vector pVT102-U. In the recombinant ILP, the C-terminus of B-domain and the N-terminus of A-domain of amphioxus ILP deduced from cDNA were linked together by a tripeptide, Ala-Ala-Lys, and its B28Arg residue was also replaced by Lys to facilitate its conversion to a double-chain form by Lys-C cleavage. The expression vector was transformed into yeast cells and the recombinant ILP was expressed efficiently. The purified single-chain and double-chain ILP was obtained by fermentation, purification and enzymatic cleavage. Molecular weight measurement and amino acid composition analysis showed that the primary structure of ILP was correct. Circular dichroism analysis showed that the secondary and tertiary structure of double-chain ILP was similar to that of insulin, while double-chain ILP had no measurable insulin activity in insulin receptor binding assay. Additionally, New Zealand Rabbits were immunized with single-chain ILP and high titre polyclonal antibody was obtained. This work was important for further investigating the molecular evolution of insulin and IGF-1 and the distribution and existence of ILP in amphioxus.