In vitro activity of a recombinant ABC transporter protein in the processing of plantaricin E pre-peptide

Most bacteriocins of lactic acid bacteria (LAB) are initially synthesized as pre-peptides with an N-terminal extension (leader peptides). Generally, the precursor peptides containing a double-glycine-type leader are processed by a dedicated ATP-binding cassette (ABC) transporter. The ABC transporter and an accessory protein lead to the cleavage of inactive pre-peptide with the concomitant export of the mature peptide across the cytoplasmic membrane. Plantaricins E, F, J, and K belong to class IIb 2-peptide bacteriocins and are synthesized as pre-peptides containing N-terminal G-G leader peptide. In this study, the heterologous expression, purification, and characterization of PlnE pre-peptide, ABC transporter (PlnG), and accessory protein (PlnH) from Lactobacillus plantarum LR/14 in Escherichia coli BL21 (DE3) strain were reported. An in vitro assay was conducted with the inactive PlnE pre-peptide, which after cleavage by the addition of ABC transporter protein exhibited antimicrobial activity against some LAB species. The activity of cleaved pre-peptide was comparable to the activity of mature peptide. Accessory protein was also heterologously expressed and purified; however, no effect on processing activity was detected by the addition of the accessory protein, which suggests that accessory protein is not involved in cleavage, but it might help in the transport of mature plantaricins across the membrane.