Expression of Enterocin A in Saccharomyces cerevisiae

Recombinant expression in the yeast Saccharomyces cerevisiae offers an alternative approach to developing large-scale production systems for class II bacteriocins from lactic acid bacteria, such as enterocin A, mundticin ST4SA and plantaricin 423. An important consideration for bacteriocin activity is disulphide bond formation: mature mundticin ST4SA has one, and plantaricin 423 and enterocin A each have two disulphide bonds. The native bacteriocin operon typically includes accessory proteins that facilitate disulphide bond formation, but this gene is absent in the enterocin A operon. In this study, the recombinant expression of a codon-optimised gene for enterocin A in S. cerevisiae, was compared to that for a codon-optimised plantaricin 423 and mundticin ST4SA, previously successfully expressed in S. cerevisiae. Shake flasks delivered more than twofold higher peptide EntA_Opt levels than PlaX_Opt and MunX_Opt, with even higher EntA_Opt expression levels in batch fermentations. However, the bacteriocin activity of plantaricin 423 was considerably lower than that of enterocin A and mundticin ST4SA. It is postulated that this could be a result of incorrect disulphide bond conformation due to the absence of the plantaricin accessory protein, PlaC, in S. cerevisiae. Nano-LC-MS/MS analysis showed various post-translational modifications for the peptides, with a greater proportion of EntA_Opt peptides with the correct disulphide bond conformation than for PlaX_Opt. This study demonstrated that S. cerevisiae is a promising host to produce recombinant class IIa bacteriocins, particularly enterocin A. However, the co-expression of accessory proteins should be investigated to improve the activity of recombinant plantaricin 423.