STRUCTURAL AND FUNCTIONAL CHARACTERISATION OF MUCUS ADHESION PROTEINS OF LACTOBACILLUS REUTERI

Mucus is the first point of contact between the gut microbiota and the host. Mucus adhesins are thought to be key mediators in the mucus adhesion of commensal Lactobacillus species. However, knowledge on the structural or functional basis of adhesin interaction with mucin glycoproteins, the main component of mucus, is limited. This work describes the biochemical and structural properties of two cell-surface proteins from Lactobacillus reuteri, the mucus-binding protein (MUB) and the Lar0958 protein, and their mucin binding ability. MUB from L. reuteri ATCC 53608 consists of 14 Mub repeats, six type 1 and eight type 2. Single and tandem Mub repeats were heterologously expressed and purified for structural and functional studies. The three-dimensional structure of the Mub type 1 MubRV was determined by X-ray crystallography and revealed two structural domains, B1 and B2. Furthermore, structural homology between MubRV and fibre-like adhesins of Gram-positive pathogens was identified. Small angle X-ray scattering experiments of single and tandem Mub repeats suggested an elongated structure of MUB in a ‘beads on a string’ arrangement. Functional studies of recombinant Mub repeats and the full-length native MUB isolated from Lactobacillus spent culture media, demonstrated binding to different mucins in vitro. Sugar inhibition experiments and glycan arrays suggested the involvement of sugar recognition in MUB protein binding to mucins. Lar0958 is a modular protein of six Lar0958 repeats present on the cell-surface of L. reuteri DSM 20016T. The crystal structure of a single recombinant Lar0958 repeat was solved at 1.5 Å, demonstrating a similar protein fold to Mub repeats. In addition, the Lar0958 repeat shows structural similarity to internalin proteins of the pathogen Listeria monocytogenes. Taken together these results provide new insights into the structural organisation of lactobacilli mucus adhesins and their interaction with mucins, highlighting similarities with Gram-positive adhesins of pathogenic bacteria.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2013

Author dc:creator

• Etzold, Sabrina

Language dc:language

en