Optimization of transpeptidation reaction of the insulin precursor for efficient yield recovery during downstream processing

Abstract

Nowadays Yeast cell is a popular host for recombinant human insulin production where initially it secrets insulin precursor fusion protein with N-terminal spacer peptide and deletedthreonineB30, followed by a small C-peptide connected with its A andB chains. The insulin precursor is then purified and subsequently converted into human insulin ester via a slow transpeptidation reaction (hydrolysis and coupling) in presence of both trypsin and O-tert-Butyl-L-threonine –tert-butyl ester (O-Thr-ester). Transpeptidation reaction is very critical for recovery of insulin at the least expenses of the aforementioned chemicals. In this study a protocol has been developed where certain parameters have been changed in congruence with published data. The major focus was to use low amount of trypsin and O-Thr-ester for the transpeptidation reaction as well as changing organic solvent composition, water content, pH, time and temperature. In this study, a two-step transpeptidation reaction has been proposed instead of one-step reaction process by separating the cleavage step from the coupling step so that each reaction was performed under its optimal condition. Through this method, the total the conversion of insulin ester increased 57.44% and the reaction time was reduced 58.33% by using the same amount of trypsin and O-Thr-ester compared with the one-step method and available published data. Thus, this two-step transpeptidation strategy was simple, efficient, suitable for scale-up and cost effective and could be used for the pharmaceutical production of human insulin.