05 September 2018

Scientists have identified new powerful enzymes that can remove sugars from the A or B antigens on red blood cells and convert them into type O blood, a major conference has heard.

Dr Stephen Withers, of the University of British Columbia, Canada, and colleagues believe that these enzymes are up to 30 times better at performing this conversion than previously studied enzymes.

Type O blood can be given to anyone who needs a blood transfusion, so it is often used in emergencies or in times of high demand in hospitals. One method which has been put forward to keep up with this demand is to convert Type A or B blood into Type O. The difference between the antigens found on Type A or B red blood cells and the Type O blood antigen is just one sugar molecule. Therefore, removing the additional sugar from the A or B antigen should in theory be enough to convert those blood types into type O.

Enzymes are well-placed to perform this conversion, but these enzymes need to be both safe and economical. To identify potential enzyme candidates, the team sampled the genes of millions of microorganisms without needing to isolate the individual species, using a technique called metagenomics. By selecting for DNA containing genes that code for enzymes they found these new 'biocatalysts'.

Dr Withers said: "This is a way of getting that genetic information out of the environment and into the laboratory setting and then screening for the activity we are interested in."

The team ultimately found successful candidate enzymes in the human gut microbiome. Proteins called mucins, which line the gut wall, have extensive structures made of sugar molecules attached to them, which gut bacteria can anchor themselves onto and use as a food source.

A sub-category of these mucin sugars has a similar structure to the antigens on A and B type blood, so the researchers focused on the enzymes the bacteria use to remove the sugars from mucins.

This led to the discovery of a new family of enzymes that are highly effective at removing sugars from Type A antigens. That these enzymes are as much as 30 times more efficient than ones previously studied means that smaller quantities can be used, which has two advantages for translation into the clinic. Firstly, using less is more economical, and secondly, it would be easier to remove any leftover enzyme from the blood before it is transfused, reducing the chance of adverse immune reactions against these bacterial enzymes.

The enzymes are now being evaluated on a larger scale for potential clinical testing. Previous research by others had already found enzymes that could efficiently convert Type B antigens to Type O, though Dr Withers and his team are also hoping to find even more efficient versions.

“I am optimistic that we have a very interesting candidate to adjust donated blood to a common type,” Withers says. “Of course, it will have to go through lots of clinical trials to make sure that it doesn’t have any adverse consequences, but it is looking very promising.”

The unpublished findings were presented at the National Meeting & Exposition of the American Chemical Society, held in Boston, USA.

Source: Withers, S. et al. Discovery of CAZYmes for cell surface glycan removal through metagenomics: Towards universal blood. Presented on 21 August 2018 at the National Meeting


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