Generation of Active Trypsin by Chemical Cleavage

A novel strategy has been developed to generate trypsin from trypsinogen without proteolytic processing. The unnatural amino acid allylglycine was incorporated into a trypsinogen variant to permit cleavage specifically at Ile-16, the prototypical activation site, and generate the active protease, trypsin. A suppressor tRNA, activated with allylglycine, was used to synthesize the allylglycine trypsinogen variant by in vitro translation of an mRNA transcript that placed the UAG stop codon immediately prior to the authentic trypsin coding region. Iodine treatment of the variant trypsinogen resulted in trypsin that was fully active and kinetically indistinguishable from wild type recombinant trypsin. Using single substrates, the iodine treated variant exhibited a catalytic profile essentially identical to that of wild type recombinant rat trypsin (kcat/KM=3.7±0.5 vs 3.7±0.8 μM−1s−1, respectively). Furthermore, the specificity profiles generated from substrate combinatorial libraries are indistinguishable. These results illustrate that (1) iodine activated allylglycine trypsinogen is virtually identical to enteropeptidase activated recombinant trypsinogen and (2) this novel technique is a feasible alternative to achieve site specific cleavage of serine protease zymogens.