New semi-synthesis of ubiquitin C-terminal conjugate with 7-amino-4-methylcoumarin

The ligation of peptide hydrazides at a Gly site carrying a removal auxiliary was found to be an efficient process. This technology was successfully used for the synthesis of ubiquitin C-terminal conjugates. Recombinant Ub(1-75)-NHNH₂ was prepared through the hydrozinolysis of the Ub(1-75)-intein fusion protein. It was ligated with a glycine derivative modified with an acid-sensitive thiol auxiliary. The final acid treatment produced the desired bioactive ubiquitin conjugates in practical quantities. Thus, the method described here extends the protocols of expressed protein ligation.