In-vivo processing of the initiator methionine from recombinant methionyl human interleukin-6 synthesized in Escherichia coli overproducing aminopeptidase-P.

Human interleukin 6 (hIL-6) overproduced in Escherichia coli HB101 was found to partially retain the initiator methionine (Met) residue (Met-hIL-6). In order to remove the residual N-terminal Met in vivo, an attempt was made to express hIL-6 in aminopeptidase-P (Ap-P)-hyperproducing strains, since the N-terminus Met-Pro- structure of nascent recombinant hIL-6 has been shown to be a favoured substrate of the enzyme in vitro. Using a mutant with duplicated Ap-P genes (pepP) on a chromosome or some recombinant strains overproducing Ap-P, we have succeeded in removing the initiator Met from Met-hIL-6 in vivo. The content of the mature product without the initiator Met in the pepP recombinant strains could be increased to approximately 99% from 85%.