Lactobacillus gasseri LA39 and L. reuteri LA6 isolated from feces of the same human infant were found to produce similar cyclic bacteriocins (named gassericin A and reutericin 6, respectively) that cannot be distinguished by molecular weights or primary amino acid sequences. However, reutericin 6 has a narrower killing spectrum than gassericin A. Gassericin A inhibits the growth of L. reuteri LA6, but reutericin 6 does not inhibit the growth of L. gasseri LA39. Both bacteriocins cause potassium ion efflux from indicator cells and liposomes, but the amounts of efflux and patterns of action are different. Although circular dichroism spectra of purified bacteriocins revealed that both antibacterial peptides are composed mainly of alpha-helices, the spectra of the bacteriocins differ. The results of D- and L-amino acid composition analysis showed that two residues and one residue of D-Ala were detected among 18 Ala residues of gassericin A and reutericin 6, respectively. The different D-alanine contents of the bacteriocins may cause the differences in modes of action, amounts of potassium ion efflux, and secondary structures (Kawai et al., 2004).
Homologous of Gassericin includes AcidocinB of Lactobacillus acidophilus (91aas; almost identical to gassericin) and Butyrivibiocin of Butyrivibrio fibrisolvens (80aas).
The generalized reaction catalyzed by gassericin is:
small molecules (in) small molecules (out)