Identification of WxL and S-Layer Proteins from Lactobacillus brevis with the Ability to Bind Cellulose and Xylan

Xylanase releases xylo-oligosaccharides from dietary xylan, which stimulate the growth of the gut bacteria lactobacilli. Many lactobacilli adhere to dietary fibers, which may facilitate the assimilation of xylo-oligosaccharides and help them gain competence in the gut, but the underlying mechanisms remain elusive. Herein we report, from the highly abundant transcripts of Lactobacillus brevis cultured in wheat arabinoxylan supplemented with a xylanase, the identification of genes encoding four putative cell-surface WxL proteins (Lb630, Lb631, Lb632, and Lb635) and one S-layer protein (Lb1325) with either cellulose- or xylan-binding ability. The repetitively occurring WxL proteins were encoded by a gene cluster, among which Lb630 was chosen for further mutational studies. The analysis revealed three aromatic residues (F30, W61, and W156) that might be involved in the interaction of the protein with cellulose. A homology search in the genome of Enterococcus faecium identified three WxL proteins with conserved counterparts of these three aromatic residues, and they were also found to be able to bind cellulose and xylan. The findings suggested a role of the cell-surface WxL and S-layer proteins in assisting the cellular adhesion of L. brevis to plant cell wall polysaccharides.

Automated summary

Xylanase releases xylo-oligosaccharides that stimulate the growth of lactobacilli in the gut. The study found that certain cell-surface WxL and S-layer proteins in Lactobacillus brevis play a role in assisting the cellular adhesion of the bacteria to plant cell wall polysaccharides. These proteins were also found to have cellulose- and xylan-binding ability.