microbiology, Vol 141, 649-654, Copyright © 1995 by Society for General Microbiology
Effects of signal peptide mutations on processing of Bacillus stearothermophilus alpha-amylase in Escherichia coli
I Suominen, P Meyer, C Tilgmann, T Glumoff, V Glumoff, J Kapyla and P Mantsala
Department of Biochemistry, University of Turku, Finland.
Bacillus stearothermophilus alpha-amylase has a signal peptide typical for
proteins exported by Gram-positive bacteria. There is only one signal
peptidase processing site when the protein is exported from the original
host, but when it is exported by Escherichia coli, two alternative sites
are utilized. Site-directed mutagenesis was used to study the processing in
E. coli. Processing sites for 13 B. stearothermophilus alpha-amylases
carrying mutations in their signal peptide were determined. Processing of
the signal peptide was remarkably tolerant to mutations, because switching
between the alternative sites was possible. The length and the sequence of
the region between the hydrophobic core and the cleavage site was crucial
for determining the choice of the processing site. Some mutations more
distal to the cleavage site also affected the site preference.
