Researchers have uncovered a protein that may help beneficial gut bacteria bind to the mucus membrane of the gastrointestinal tract enabling them to more effectively colonise and produce their health promoting effects.   It is hoped the work carried out at the Institute of Food Research (IFR), part of the Biotechnology and Biological Sciences Research Council, will help probiotic supplement manufacturers identify strains of bacteria that will provide more reliable and pronounced health benefits.

"Probiotics need to interact with cells lining the gut to have a beneficial effect, and if they attach to surfaces in the gut they are more likely to stick around long enough to exert their activity," says Dr Nathalie Juge from IFR.

The lining of the gastrointestinal (GI) tract which is made up of predominantly endothelial cells which are involved in digestion and absorption of nutrients are protected by a layer of mucus produced by specialised cells known as 'goblet cells'. As well as protecting the endothelial gut lining the mucus provides an anchoring point for beneficial bacteria that help maintain gut health and that of the body as a whole.

Beneficial bacteria, or probiotics, have been suggested to have a variety of health promoting properties from preventing and treating diarrhoea due to GI infection and providing relief from the symptoms of irritable bowel syndrome (IBS) to aiding in the maintainance of a healthy weight and the prevention of asthma and allergic conditions such as eczema and rhinitis (hayfever).

Previously very little was known about how commensal bacteria (those resident in our guts) adhered to the gut wall with research focusing on how pathogenic bacteria achieved this. Now, in a paper published in the Journal of Biological Chemistry IFR scientists have obtained the first crystal structure of a mucus-binding protein from a beneficial bacteria.

The protein was extracted from a strain of Lactobacillus reuteri, a lactic acid bacterium naturally found in the GI tract. Lactic acid bacteria are the most common microorganisms used as probiotics and strains of L. reuteri are themselves often used.

These mucus-binding proteins are more abundant in lactic acid bacteria than other types and particularly in strains that inhabit the gut. The presence of the proteins may contribute to the ability of lactic acid bacteria to interact with the host.

The IFR team found that these mucus-binding proteins also recognise human immunoglobulin proteins (antibodies). These are an integral part of the immune system. Mucus-binding proteins may therefore also play a wider role in gut and systemic health. As much as 80% of the immune system is located in the gut so the makeup of the gut flora has profound ramifications for overall health.

Probiotic manufacturers have thus far often struggled to produce supplements that are effective. Probiotic bacteria must first survive the manufacturing process, shipping and storage before the capsule or poweder is even swallowed. They must then survive the harsh acidic environment of the stomach and the digestive enzymes present in the small intestine. Finally they must adhere to the gut lining long enough to produce results.

The discovery of this mechanism by which beneficial bacteria adhere to the gut lining is another step to producing more effective probiotic products.

"The strain-specificity of these proteins demonstrates the need for the careful molecular design and selection of probiotics," says Dr Juge. This also opens new avenues of research to study the fundamental roles bacteria play in the gastrointestinal tract.”

Source: MacKenzie DA Tailford LE Hemmings AM Juge N (2009) Crystal structure of a mucus-binding protein repeat reveals an unexpected functional immunoglobulin binding activity Journal of Biological Chemistry 284(47):32444-53

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