Abstract
BackgroundSignal peptide peptidases play an important role in the removal of remnant signal peptides in the cell membrane, a critical step for extracellular protein production. Although these proteins are likely a central component for extracellular protein production, there has been a lack of research on whether protein secretion could be enhanced via overexpression of signal peptide peptidases.ResultsIn this study, both nattokinase and α-amylase were employed as prototypical secreted target proteins to evaluate the function of putative signal peptide peptidases (SppA and TepA) in Bacillus licheniformis. We observed dramatic decreases in the concentrations of both target proteins (45 and 49%, respectively) in a sppA deficient strain, while the extracellular protein yields of nattokinase and α-amylase were increased by 30 and 67% respectively in a strain overexpressing SppA. In addition, biomass, specific enzyme activities and the relative gene transcriptional levels were also enhanced due to the overexpression of sppA, while altering the expression levels of tepA had no effect on the concentrations of the secreted target proteins.ConclusionsOur results confirm that SppA, but not TepA, plays an important functional role for protein secretion in B. licheniformis. Our results indicate that the sppA overexpression strain, B. licheniformis BL10GS, could be used as a promising host strain for the industrial production of heterologous secreted proteins.
Highlights
Signal peptide peptidases play an important role in the removal of remnant signal peptides in the cell membrane, a critical step for extracellular protein production
Establishment of the signal peptide peptidase gene deficient strains Based on the genome sequence and annotation of B. licheniformis WX-02, two genes were predicted to function as Signal peptide peptidase (SPP) in B. licheniformis WX-02 [28]
In order to investigate the function of these gene products, sppA and tepA were deleted in the parent strain B. licheniformis BL10, respectively
Summary
Signal peptide peptidases play an important role in the removal of remnant signal peptides in the cell membrane, a critical step for extracellular protein production. B. licheniformis BL10 was constructed as a highly efficient host strain for protein production by knocking out ten genes coding for extracellular proteases (Mpr, Vpr, AprX, Epr, Bpr, WprA, AprE, BprA), flagellin and amylase in B. licheniformis WX-02. Using this engineered B. licheniformis BL10, a previous study has demonstrated that nattokinase activity could be increased by 39% [7].
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