Specific degradation of the mucus adhesion-promoting protein (MapA) of Lactobacillus reuteri to an antimicrobial peptide

Abstract

The intestinal flora of mammals contains lactic acid bacteria (LAB) that may provide positive health effects for the host. Such bacteria are referred to as probiotic bacteria. From a pig, we have isolated a Lactobacillus reuteri strain that produces an antimicrobial peptide (AMP). The peptide was purified and characterized, and it was unequivocally shown that the AMP was a well-defined degradation product obtained from the mucus adhesion-promoting protein (MapA); it was therefore termed AP48-MapA. This finding demonstrates how large proteins might inherit unexpected pleiotropic functions by conferring antimicrobial capacities on the producer. The MapA/AP48-MapA system is the first example where a large protein of an intestinal LAB is shown to give rise to such an AMP. It is also of particular interest that the protein that provides this AMP is associated with the binding of the bacterium producing it to the surface/lining of the gut. This finding gives us new perspective on how some probiotic bacteria may successfully compete in this environment and thereby contribute to a healthy microbiota.

FIG. 1.

Mass spectrometry results for the fraction (nr 24) with the highest antimicrobial activity. Intens., intensity; a.u., arbitrary units.

FIG. 2.

(A) Amino acid sequence of the MapA protein. (B) Truncated peptides of MapA, whose molecular weights (MW) matched well with the molecular masses of the purified peptides determined by mass spectrometry. MapA (accession no. AJ293860) is a mucus adhesion protein (263 aa) containing a sec leader sequence (underlined). Note that all truncated peptides have a common N terminus, but each has a different C terminus. Bold letters indicate the sequence determined by chemical sequencing of purified peptides.