ABSTRACT
Modification of substrate specificity of an autoprocessing enzyme is accompanied by a risk of significant failure of self-cleavage of the pro-region essential for activation. Therefore, to enhance processing, we engineered the pro-region of mutant subtilisins E of Bacillus subtilis with altered substrate specificity. A high-activity mutant subtilisin E with Ile31Leu replacement (I31L) as well as the wild-type enzyme show poor recognition of acid residues as the P1 substrate. To increase the P1 substrate preference for acid residues, Glu156Gln and Gly166Lys/Arg substitutions were introduced into the I31L gene based upon a report on subtilisin BPN' [Wells et al. (1987) Proc. Natl. Acad. Sci. USA 84, 1219-1223]. The apparent P1 specificity of four mutants (E156Q/G166K, E156Q/G166R, G166K, and G166R) was extended to acid residues, but the halo-forming activity of Escherichia coli expressing the mutant genes on skim milk-containing plates was significantly decreased due to the lower autoprocessing efficiency. A marked increase in active enzyme production occurred when Tyr(-1) in the pro-region of these mutants was then replaced by Asp or Glu. Five mutants with Glu(-2)Ala/Val/Gly or Tyr(-1)Cys/Ser substitution showing enhanced halo-forming activity were further isolated by PCR random mutagenesis in the pro-region of the E156Q/G166K mutant. These results indicated that introduction of an optimum arrangement at the cleavage site in the pro-region is an effective method for obtaining a higher yield of active enzymes.
Subject(s)
Bacillus subtilis/enzymology , Mutation/genetics , Protein Engineering , Subtilisins/chemistry , Subtilisins/metabolism , Amino Acid Sequence , Amino Acid Substitution/genetics , Bacillus subtilis/cytology , Electrophoresis, Polyacrylamide Gel , Enzyme Activation , Escherichia coli , Glutamine/genetics , Glutamine/metabolism , Hydrolysis , Kinetics , Leucine/genetics , Leucine/metabolism , Periplasm/enzymology , Substrate Specificity , Subtilisins/geneticsABSTRACT
An efficient procedure was established to select for thermostable proteases in an extreme thermophile, Thermus thermophilus. A non-protease-secreting mutant derived from T. thermophilus TH125 was used as host and the expression plasmid for aqualysin I from T. aquaticus YT-1 was constructed as a source of thermostable protease. T. thermophilus cells harboring the recombinant plasmid produced active aqualysin I into the medium and were able to grow on a minimal medium containing milk casein as the sole source of carbon and nitrogen.
