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Fighting Celiac Disease: Improvement of pH Stability of Cathepsin L In Vitro by Computational Design
Roughly 1% of the global population is susceptible to the celiac disease (CD) — inheritable autoimmune inflammation of the small intestine, caused by intolerance to gliadin proteins present in wheat, rye and barley grains, and called gluten in wheat. Classic treatment is a life-long gluten-free diet, which is constraining and costly. Alternative approach is based upon development and oral reception of the effective peptidases that degrade in the stomach immunogenic proline- and glutamine-rich gliadin peptides, which cause the severe reaction in the intestine. In the previous research we have established that the major digestive peptidase of an insect Tribolium castaneum — cathepsin L — hydrolyzes immunogenic prolamins after Gln residues; although, this enzyme is unstable in the extremely acidic environment (pH 2–4) of the human stomach and cannot be used as the digestive aid. In this work, using molecular dynamics simulations, we discover the probable cause of pH-instability of cathepsin L — loss of the catalytically-competent rotameric state of one of the active site residues, His 275. Trying to “fix” the correct orientation of this residue, we suggested a V277A mutant variant, which extended the range of stability to the acidic environment, retaining the most of activity. We suggest this protein as a lead glutenase for the development of oral medical preparation that fights CD and gluten intolerance in the susceptible people.