Proteinase inhibitory activity of recombinant rabbit α-1-antiproteinases expressed in Escherichia coli

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The S-22 form of rabbit α-1-antiproteinase (α-1-antitrypsin), having tyrosine at the reactive site, was isolated from a rabbit liver cDNA library, sequenced and expressed in Escherichia coli. The recombinant fusion protein of the S-22 form with maltose binding protein did not inhibit elastase, trypsin, or chymotrypsin. However, the fusion proteins of the F isoform of rabbit a-1-antiproteinase and human α-1-antitrypsin inhibited those proteinases. The expression plasmid harboring cDNA for the S-22 and F forms were excised with BbsI and the resulting 0.5 kbase fragments were exchanged and ligated. The plasmids having a chimera sequence of the S-22 and F forms were expressed and the fusion proteins were examined for proteinase inhibitory activity. One of the fusion proteins, having 88 amino acids of the F form in the C-terminal region including the reactive site loop, inhibited the proteinases but the other one with the C-terminal sequence of the S-22 form lost the inhibitory activity.