An efficient trypsin digestion strategy for improving desB30 productivity from recombinant human insulin precursor fusion protein

Improving production of Streptomyces griseus trypsin for enzymatic processing of insulin precursor

Background

Trypsin has many applications in food and pharmaceutical manufacturing. Although commercial trypsin is usually extracted from porcine pancreas, this source carries the risks of infectivity and immunogenicity. Microbial Streptomyces griseus trypsin (SGT) is a prime alternative because it possesses efficient hydrolysis activity without such risks. However, the remarkable hydrolysis efficiency of SGT causes autolysis, and five autolysis sites, R21, R32, K122, R153, and R201, were identified from its autolysate.

Results

The tbcf (K101A, R201V) mutant was screened by a directed selection approach for improved activity in flask culture (60.85 ± 3.42 U mL⁻¹, increased 1.5-fold). From the molecular dynamics simulation, in the K101A/R201V mutant the distance between the catalytical residues D102 and H57 was shortened to 6.5 Å vs 7.0 Å in the wild type, which afforded the improved specific activity of 1527.96 ± 62.81 U mg⁻¹. Furthermore, the production of trypsin was increased by 302.8% (689.47 ± 6.78 U mL⁻¹) in a 3-L bioreactor, with co-overexpression of chaperones SSO2 and UBC1 in Pichia pastoris.

Conclusions

SGT protein could be a good source of trypsin for insulin production. As a result of the hydrolysates analysis and direct selection, the activity of the tbcf (K101A, R201V) mutant increased 1.5-fold. Furthermore, the production of trypsin was improved threefold by overexpressing chaperone protein in Pichia pastoris. Future studies should investigate the application of SGT to insulin and pharmaceutical manufacturing.

Intein-mediated recombinant expression of monomeric B22Asp desB30 insulin

BACKGROUND

Insulin controls hyperglycemia caused by diabetes, and virtually all treatments require exogenous insulin. However, the product's extensive post-translational modifications have hindered the manufacture of recombinant insulin.

RESULT

Here we report a novel production method for a monomeric B22Asp desB30 insulin analog (B22D desB30 insulin). Its precursor, DPIP, is fused to an N-terminal chitin-binding domain and intein self-cleavage tag. The fusion protein is expressed and purified from E. coli and immobilized on chitin resins. DPIP is then released using an optimized pH shift and converted to mature insulin via trypsin digest. The resulting product appears monomeric, > 90% pure and devoid of any exogenous enzyme.

CONCLUSION

Thus, biologically active insulin analog can be efficiently produced in bacteria and potentially applicable in the treatment of human diabetes.

A Simplified and Efficient Process for Insulin Production in Pichia pastoris

A significant barrier to insulin is affordability. In this manuscript we describe improvements to key steps in the insulin production process in Pichia pastoris that reduce cost and time. The strategy for recovery and processing of human insulin precursor has been streamlined to two steps from bioreactor to the transpeptidation reaction. In the first step the insulin precursor secreted during the methanol induction phase is recovered directly from the culture broth using Tangential Flow Filtration with a Prostak^™ module eliminating the laborious and time-consuming multi-step clarification, including centrifugation. In the second step the protein is applied at very high loadings on a cation exchange resin and eluted in a mixture of water and ethanol to obtain a concentrated insulin precursor, suitable for use directly in the transpeptidation reaction. Overall the yield from insulin precursor to human insulin was 51% and consisted of three purification chromatography steps. In addition we describe a method for recovery of the excess of H-Thr(tBu)-OtBu from the transpeptidation reaction mixture, one of the more costly reagents in the process, along with its successful reuse.

Two-step transpeptidation of the insulin precursor expressed in Pichia pastoris to insulin ester via trypsin-catalyzed cleavage and coupling

Insulin precursor fusion protein expressed in Pichia pastoris is a single-chain protein with a spacer peptide (EEAEAEAEPK) localized at its N-terminal. Currently, the one-step transpeptidation reaction with low yield and high cost is generally employed to convert the insulin precursor fusion protein into human insulin ester. In this study, a two-step transpeptidation reaction was proposed separating the cleavage step from the coupling step so that each reaction was performed under its optimal conditions. Using this method, the total efficiency doubled and the reaction time was shortened compared with the one-step method. In addition, the amount of O-t-butyl-l-threonine t-butyl ester and trypsin dosages were reduced by 50% and 75%, respectively. This two-step transpeptidation strategy was simple and efficient and could be used for the pharmaceutical production of human insulin.