Written using 2 laptops and a smartphone, with no lack of lost drafts and swearing (it’s been a trying one this week!), here we are – my second full article. This week: Biochemistry – enjoy!
Scientists in America have designed a potential treatment for Coeliac disease. The condition is characterised by an intolerance to gluten, a common protein in wheat, barley and rye. In most cases, the symptoms, if any, vary from mild stomach cramps to vomiting and diarrhoea, meaning sufferers need to stick to a completely gluten-free diet for their entire lives. That means no bread, cakes, beer and far more besides, unless they can buy gluten-free alternatives. As such, treatments for the disease have long been sought after.
Gluten is actually made up of multiple proteins. When eaten, it is broken down in the stomach into these separate proteins, one of which is called α-gliadin. Whilst some of it can be degraded, a section of this protein’s structure prevents enzymes from breaking it down any further and it passes through to the small intestine partially intact. In Coeliac disease sufferers, an enzyme called tissue transglutaminase then binds to the unbreakable part of the α-gliadin, triggering a response by the immune system, which thinks the enzyme-protein complex is harmful. As part of this response, the intestinal wall becomes inflamed, meaning it functions less effectively. It absorbs less water than normal, very quickly resulting in diarrhoea as that water passes through the digestive tract. Also, unfortunately in this case, the body’s evolved response to any kind of ingested ‘toxin’ is to induce vomiting. As such, the most unfortunate sufferers should probably find a bathroom with a lavatory and wash basin quite close together…
It has long been thought that a treatment for Coeliac disease could be an enzyme that targets the unbreakable section of α-gliadin molecules and degrades them completely. However, given that it is a disorder of the digestive system, it is expected that any effective therapy would need to be delivered orally. Such an enzyme would have to fulfil 3 key criteria to work as intended:
- It must be at its most effective in the temperature and acidic conditions of the stomach after a meal
- It must be resistant to natural digestive enzymes so it won’t be broken down
- It must be able to break down the problematic region in α-gliadin and nothing else
Previous efforts have begun with enzymes that act specifically on the problematic region of α-gliadin and then tried to alter them to work in acidic conditions. Unfortunately, few have been particularly effective. Conversely, the group behind this latest breakthrough started with an enzyme that works in acidic conditions and adapted it so it binds to, and degrades, α-gliadin rather than the molecule it originally acted upon. This is rather like taking a key that unlocks one door and cutting and reshaping it until it fits a different keyhole entirely. An enzyme should only be able to slot into the keyhole, or ‘active site’, of the particular protein it is designed to target, otherwise other proteins may be unintentionally degraded, which can be damaging.
The group took an enzyme from the bacterium Alicyclobacillus sendaiensis and, using computer modelling software, calculated what mutations they would need to introduce into the enzyme’s structure to make it specific for α-gliadin (rather like working out where to cut and add bits onto a key). The final enzyme they produced – dubbed ‘KumaMax’ – contained 7 mutations and was 116 times more effective than it was originally and 877 times more likely to bind to the α-gliadin in the correct place, as well as being resistant to degradation by other enzymes. When compared, it also proved to be far more effective than two of the enzymes identified using the more conventional method described earlier.
Whilst not a guaranteed success at such an early stage, this enzyme’s promising start has encouraged the research group to start work on improving it further still with an eye on a future application as a therapy for Coeliac disease. We’ll have to wait and see how this pans out but the techniques applied here are certainly encouraging when we consider the number of other conditions that could benefit from such research protocols.
Refers to: Gordon et al. (2012). Computational Design of an α-Gliadin Peptidase. Am. Chem. Soc. 134, 20513-20520.