Cloning, expression and purification of the immunity factor associated with leucocin A production.
Leucocin A is a bacteriocin produced by Leucoconostoc gelidium UAL 187-22. Bacteriocin producer strains possess an immunity protein, which enables the strain to protect itself against its own bacteriocin. The immunity gene from Leucoconostoc gelidium was isolated via PCR from a recombinant clone pJF5.5. This fragment was cloned by amplifying the immunity gene from pJF5.5 and ligating it into pMALc2. The resulting recombinant plasmid pKP1 was then transformed into Escherichia coli strain JM103. The clone putative, was confirmed by DNA sequencing and southern blot hybridization using the primers EAL-2 and EAL-3. It was shown to contain an insert of 3.6 kb. Expression analysis showed the construct as an in frame malE fusion protein expressed within E. coli. The fusion construct was isolated by affinity chromatography. Leucocin A was purified to 90% purity, from the supernatant of Leucocnostoc gelidium UAL 187-22 by ion-exchange chromatography and HPLC. It was found to elute from a C18 reverse phase column at 55% actetonitrile, 0.1% TFA. Binding interaction and the stability of the immunity gene fusion protein were compared using a Biacore 2000. The supernatant and cytoplasmic extract isolated from Leucocnostoc gelidium UAL 187-22 were tested for interaction with the fusion construct. Surface Plasmon resonance studies indicated that there was no binding partner present in the supernatant which would influence the immunity process. However, a stable interaction was found between the immunity protein and an orphan ligand within the cytoplasm.