Enhanced secretion of beta-lactamase on structural modification of the Bacillus subtilis alpha-amylase signal peptide

Prediction of the secondary structure, a sequence of 33 amino acids, for the Bacillus subtilis alpha-amylase signal peptide suggested the presence of a beta-turn structure in it. Through substitution of Gly27 and/or Pro28 with Ala residues by means of the site-directed mutagenesis method, the secondary structure was predicted to consist of an alpha-helix conformation throughout the signal peptide containing a small region of random coil. The effect of the structural modification upon the secretion of proteins was analyzed as to the production of beta-lactamase after the DNA regions encoding the parental and modified signal peptides had been fused in frame to the DNA fragment for the beta-lactamase using HindIII linker DNA. The production of beta-lactamase increased to 4 to 6 times in B. subtilis cells and to 1.5 to 2.0 times in Escherichia coli with the modified signal peptides. The modification of the signal peptide affected the transcription level of the fused genes.