UK researchers based in the Institute of Food Research and the University of East Anglia have obtained the first crystal structure of a mucus-binding protein (MUB) from a strain of Lactobacillus reuteri, a lactic acid bacterium naturally found in the gastrointestinal tract, and they say that it can help explain how gut bacteria bind to the tract.
The team’s findings, which have been published in the Journal of Biological Chemistry, show these mucus-binding proteins are more abundant in lactic acid bacteria than other types and the knowledge derived could help in selecting strains for use as probiotics in foods and supplements.
Lactic acid bacteria are the most common microorganisms used as probiotics.
The researchers said that the cells lining the gut are covered in a protective layer of mucus which also provides an attachment site for beneficial bacteria that help maintain normal gut function.
Probiotics need to interact with cells lining the gut to have a beneficial effect, so if they attach to surfaces in the gut they are more likely to exert their activity for a longer time frame, they added.
But the researchers explained that while mucus adhesion has been well studied for pathogenic bacteria, precisely what enables commensal (gut bacteria) bacteria to stick is not known, as the limited availability of mucus and mucus-producing cell lines has restricted previous research on the subject.
Lead researcher Dr Nathalie Juge told NutraIngredients.com that the crystal structure they have obtained can now give insight into the type of receptors likely to be recognised by the bacteria in the mucus layer.
“In addition the knowledge of 3D structure may help to identify proteins with similar functions which may not be identifiable based on genome sequence only,” she continued.
Juge emphasises that their results show that there is a need for careful selection/design of probiotics based on molecular knowledge because “the attachment of bacteria to mucus seems to be molecule specific (via different type of mucus-binding proteins or other factors) and strain specific (MUBs present in L reuteri 1063 not 1050 for example).”
However, she explained that while certain strains do possess the genes encoding MUB it may be that the protein is not expressed, or not functional depending on gut conditions or the food matrix source of the strains.
The scientists also found that these mucus-binding proteins recognise human immunoglobulin (Igs) proteins, which are an integral part of the immune system.
Mucus-binding proteins may therefore also play a wider role in gut health as a site of attachment for bacteria, reported the researchers.
Source: Journal of Biological Chemistry
Published online ahead of print
Title: Crystal Structure of a Mucus-binding Protein Repeat Reveals an Unexpected Functional Immunoglobulin Binding Activity
Authors: D. A. MacKenzie, L E. Tailford, A M. Hemmings, N. Juge