Introduction of spacer peptides N-terminal to a cleavage recognition motif in recombinant fusion proteins can improve site-specific cleavage.

To improve site-specific cleavage of a methionyl porcine growth hormone [[Met1]-pGH(1-46)-IGF-II] fusion protein by the enzyme H64A subtilisin, a series of flexible, unstructured spacer peptides were introduced N-terminal to the cleavage site. When enzymatic digestion preceded refolding of the fusion proteins, IGF-II could only be liberated from substrates which contained spacer peptides. Compared with the parent construct, the yield of IGF-II from refolded fusion proteins containing spacers was improved up to two-fold. Furthermore, this cleavage rate was improved by removing a competing protease recognition motif from the fusion partner. These data show that fusion partners can influence site-specific proteolysis of fusion proteins. Introduction of flexible spacers between the moieties can alleviate these interactions.