CIC bioGUNE researchers have opened a new pathway for the future development of biosensors that enable measuring the glucose in the blood, but which are also believed to be more reliable with other fluids, such as urine. To this end, a complex scientific process has been developed which has called into question a dominant paradigm amongst the scientific community with respect to the mechanisms of binding and communication between proteins.
The mechanisms of communication at subcellular level are based on the interaction between proteins or between proteins and metabolites and other ligands. These phenomena help to explain the immense majority of protein functions in living organisms, but it is essential to this end that each protein knows exactly to which ligand it has to bind.
To date it has been widely accepted within the scientific community that there was a double binding mechanism between proteins, differentiated and isolated like two independent processes: some proteins bind with just one mechanism known as 'induced fit' (the protein takes the shape of the ligand during the association process), while others do so exclusively through a mechanism known as 'conformational selection' (in the same way that each lock requires a key with specific characteristics, the bind between a protein and a ligand will depend if their shapes make such a fit possible).
However, in this research, Dr. Oscar Millet, from the Structural Biology Unit at CIC bioGUNE, and published in the November issue of the Journal of the American Chemical Society, refutes this paradigm and puts forward the idea that slight modifications using genetic engineering introduced into the hinge regions between two proteins are sufficient to alter the binding mechanism itself.
For the development of this research, two bacterial periplasmic binding proteins were taken as a model. These proteins bind through a spectacular conformational change (closing two domains round a hinge region) and which is similar to the process that carnivorous plants use to trap insects between their fleshy lobes.
"The main result of our work has shown that both mechanisms are intimately connected and that we can go from one to another just by introducing small modifications in the protein," explained Óscar Millet.
"Not only have we understood this mechanism, but we have seen that the difference between this induced fit and the conformational selection is very subtle; they are actually not two independent processes - but everything is, in fact, connected. Nature is always subtle, and small variations to the chemical composition of the hinge lead us from one mechanism to the other," added the CIC bioGUNE researcher.
"This mechanism is completely governed by the hinge region to the point that by exchanging the hinges using genetic engineering, the change of mechanism also occurs: the GGBP with the RBP hinge acts through the induced fit mechanism and vice versa, and the RBP with the GGBP hinge binds to the substratum through the lock-and-key mechanism," Dr Millet explained.
"Understanding the mechanism by which periplasmic proteins trap glucose to insert it into the cells opens the possibility of using these molecules as biosensors", explained Dr Millet. Thanks to these, glucose concentration could be measured in fluids other than blood, for example urine. This would make the process easier and would provide more reliable data than the traditional glucose concentration measurement methods in the blood of diabetes patients.
The techniques currently used can only give an approximate measurement of blood glucose concentration, as there are other substances that hide it. Any advance, therefore, in the search for new diagnosis methods will improve the control of the disease.
It is very important for diabetes patients to measure their glucose concentration, as diabetes is a serious chronic disorder that affects more than 300 million people worldwide, and 5 million in Spain. This metabolic disease is caused by low production of a hormone - insulin - in the pancreas or when the body does not use this hormone properly. Insulin is involved in the transport of glucose to the interior of the cells, which turn it into useful energy.
In diabetics, the low generation of insulin or inadequate usage in the body leads to an excessive blood glucose concentration and causes many symptoms such as tiredness, weight loss, neuropathies, problems of vision and, in extreme cases, death.