Gassericin A, a bacteriocin produced by Lactobacillus gasseri LA39, has a cyclic structure linking N- and C-terminal amino acids. Gassericin A was expressed in Escherichia coli JM109 as a biotinylated fusion protein on the basis of the DNA sequence of mature bacteriocin. A positive clone accumulated the bacteriocin, with no activity, as a soluble fusion protein in the cytoplasm. After release of an N-terminal tag with factor Xa protease, gassericin A was converted into an active peptide having N- and C-termini. The total amount of purified bacteriocins (expressed and native) was 480 μg/L and 370 μg/L, respectively. However, the specific activity of expressed gassericin A was 15 AU/mg lower than that of native bacteriocin (2600 AU/mg). Although the actual Mr (molecular weight) of the expressed bacteriocin should be 5666, the peptide showed the same mobility (Mr 3800) in sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as native cyclic gassericin A, suggesting that the expressed peptide retains compact folding of the molecule similar to that of native gassericin A.
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