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J. Bacteriol., 09 1995, 5238-5246, Vol 177, No. 18
N Sauvonnet, I Poquet and AP Pugsley
Linker insertions in the pullulanase structural gene (pulA) were examined
for their effects on pullulanase activity and cell surface localization in
Escherichia coli carrying the cognate secretion genes from Klebsiella
oxytoca. Of the 23 insertions, 11 abolished pullulanase activity but none
were found to prevent secretion. To see whether more drastic changes
affected secretion, we fused up to five reporter proteins (E. coli
periplasmic alkaline phosphatase, E. coli periplasmic maltose-binding
protein, periplasmic TEM beta-lactamase, Erwinia chrysanthemi extracellular
endoglucanase Z, and Bacillus subtilis extracellular levansucrase) to three
different positions in the pullulanase polypeptide: close to the N terminus
of the mature protein, at the C terminus of the protein, or at the C
terminus of a truncated pullulanase variant lacking the last 256 amino
acids. Only 3 of the 13 different hybrids were efficiently secreted: 2 in
which beta-lactamase was fused to the C terminus of full-length or
truncated pullulanase and 1 in which maltose-binding protein was fused
close to the N terminus of pullulanase. Affinity-purified
endoglucanase-pullulanase and pullulanase-endoglucanase hybrids exhibited
apparently normal levels of pullulanase activity, indicating that the
conformation of the pullulanase segment of the hybrid had not been
dramatically altered by the presence of the reporter. However,
pullulanase-endoglucanase hybrids were secreted efficiently if the
endoglucanase component comprised only the 60-amino-acid, C-terminal
cellulose-binding domain, suggesting that at least one factor limiting
hybrid protein secretion might be the size of the reporter.
Copyright © 1995, American Society for Microbiology
Extracellular secretion of pullulanase is unaffected by minor sequence changes but is usually prevented by adding reporter proteins to its N- or C-terminal end
Unite de Genetique Moleculaire (Centre National de la Recherche Scientifique URA1149, Institut Pasteur, Paris, France.
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