Rationally engineered prolyl endopeptidases from Sphingomonas capsulata with improved hydrolytic activity towards pathogenic peptides of celiac diseases

Abstract

Celiac disease affects approximately 1% of the population and is a major public health problem worldwide. It is trigged by gluten-derived peptides, which have unusually high proline-glutamine motif content and are highly resistant to proteolysis by digestive enzymes of the gastrointestinal tract. The only treatment for celiac disease is strict, lifelong adherence to a gluten-free diet, which is effective but costly and difficult to maintain. Therefore, novel non-dietary therapies for celiac disease are urgently needed. Gluten-degrading enzymes are promising non-dietary treatments, and some enzymes have been investigated in preclinical or clinical studies. A combination of prolyl endopeptidase from Sphingomonas capsulata (SC PEP) and a glutamine-specific endoprotease (EP-B2 from barley) known as latiglutenase showed insufficient benefits in phase II clinical trials, likely because of its low enzyme activity in the gastric environment. Therefore, improving enzyme activity is essential for the clinical application of SC PEP. Enzyme activity can be enhanced using computer-aided rational protein design tools. In this study, we combined molecular docking and molecular dynamics simulation to rationally design SC PEP mutants and experimentally evaluated their activities. We identified mutants with up to 90–103% increases in specific activity and up to 80–202% increases in the catalytic rate. We have investigated the mechanism underlying the enhanced activity of these mutants, and found that a conformational transition of the β-propeller domain and catalytic domain of SC PEP was important for enzyme activity, and this transition was affected by residues in the catalytic domain and at the domain interface; a shorter distance between the substrate Pro and the oxyanion holes was also crucial for improving SC PEP catalytic activity. Our results provide useful information for the rational design of highly active SC PEPs to accelerate the development of enzyme therapeutics candidates for Celiac disease.