Scientist - News - 03-12-2009:

Protein helps probiotics stick
Beintema, Nienke

Scientists have unravelled the molecular structure of a protein that allows Lactobacillus reuteri to bind to the wall of the gastrointestinal tract. This structure also helps explain the probiotic's interaction with the immune system.

In order for probiotics to have a beneficial effect, they need to be able to stick to the wall of the gastrointestinal tract. Otherwise they would pass through the digestive system too quickly. It is still largely unknown exactly how bacteria attach to the gut, and which factors determine how well they do that. Most research has focused on this mechanism in pathogens, and only in recent years, with the increasing knowledge of beneficial bacteria, scientists have been shifting their focus to the attaching mechanisms of probiotic bacteria. This knowledge is important to understand – and possibly enhance – their beneficial effect.

Cell surface
Three scientists from the British Food Research Institute (IFR) have made an important step forward. They unravelled the molecular structure of the so-called Lactobacillus reuteri mucus-binding protein (MUB). This protein on the cell surface of L. reuteri – a popular probiotic – is involved in the interaction of the bacterium with the digestive tract. MUB, as the authors write, is representative of a broadly important class of adhesion proteins that are still relatively poorly understood. The British findings were published in the Journal of Biological Chemistry (20 November).

Immune interaction
Remarkably, as the authors note, MUB appeared to show a strong resemblance with so-called immunoglobulin (Ig)-binding proteins. Immunoglobulins, also known as antibodies, are used by the immune system to identify and neutralize pathogens. Ig-binding proteins are essential structures of the immune system. MUB's strong resemblance with these proteins allows it to 'recognize' and bind to human immunoglobulines, and thus interact with the immune function of the gut.
"The strain-specificity of these proteins demonstrates the need for the careful molecular design and selection of probiotics," said lead author Nathalie Juge in IFR's press release. "This also opens new avenues of research to study the fundamental roles bacteria play in the gastrointestinal tract."

More information:
Article in the Journal of Biological Chemistry