Characterization of a protein inhibitor of extracellular proteases produced by Erwinia chrysanthemi

Erwinia chrysanthemi, a phytopathogenic bacterium, produces a protease inhibitor which is a low-molecular-weight, heat-stable protein. In addition to its action on the three E. chrysanthemi extracellular proteases A, B and C, it also strongly inhibits the 50 kD extracellular protease of Serratia marcescens. Its structural gene (inh) was subcloned and expressed in Escherichia coli, in which it encodes an active inhibitor which was purified. The nucleotide sequence of the inh gene shows an open reading frame of 114 condons. The N-terminal amino acid sequence of the purified inhibitor was also determined. It indicated the existence of an amino-terminal signal peptide absent from the mature protein. The inhibitor is entirely periplasmic in E. chrysanthemi and partially periplasmic in E. coli.