SECRETION OF ACTIVE HUMAN MUCUS PROTEINASE-INHIBITOR BY ASPERGILLUS-NIGER AFTER KEX2-LIKE PROCESSING OF A GLUCOAMYLASE-INHIBITOR FUSION PROTEIN

We report the production of human mucus proteinase inhibitor (MPI) by the filamentous fungus Aspergillus niger to test the ability of this h ost organism to secrete low molecular weight, highly disulfide-bonded proteins in biologically active conformation. Fungal transformants hav e been obtained with an expression cassette consisting of a chimeric g ene founded on a mpi cDNA, encoding mature MPI, fused in frame to sequ ences encoding A. niger glucoamylase (glaA), separated by a KEX2-like processing sequence. Expression of the glucoamylase fusion gene in the se transformants resulted in secretion of MPI into the growth medium w ith yields up to 3 mg l(-1) N-terminal sequence analysis of the purifi ed inhibitor confirmed that the glucoamylase-MPI fusion protein was co rrectly processed to mature MPI by a KEX2-type endopeptidase present i n A. niger. Furthermore, recombinant MPI retains full inhibitory activ ity against chymotrypsin and leukocyte elastase indicating that the pr otein was folded properly. (C) 1996 Elsevier Science B.V. All rights r eserved.