Study on a prolyl endopeptidase from the skeletal muscle of common carp (Cyprinus carpio)

Substrate-like novel inhibitors of prolyl specific oligo peptidase for neurodegenerative disorders

Prolyl specific oligopeptidase (POP), is one of the highly expressed enzymes in the brain and is a prime target to treat disorders related to the central nervous system. Here, we describe the structure-based design of the tacrine derivatives, selective, and brain-permeable POP inhibitors. These compounds inactivate POP in-vitro specifically and sustainably at very low concentrations (nano molar). Among this series, compound 6b (IC50 = 0.81 ± 0.04 µM) exhibited most potent inhibition. Furthermore, kinetic study revealed that these molecules target active site of POP which is further confirmed by in-silico molecular interaction analysis. The computational docking results indicates that the compounds are well fitted in the active site with high binding score (i.e., > -7 to > -4 kcal/mol) where Trp595, Arg643, Tyr473, and Ser554 plays important role in binding with the active compounds. The molecular dynamic simulation of most active compounds (6a, 6b, 6d, and 6f) displayed higher free energy binding, when compared to the standard drug in MM-PBSA based binding free energy calculation. In addition, the predicted pharmacokinetic profile suggests that these compounds can serve as excellent inhibitors upon additional optimization which makes them prime choice for further investigation.Communicated by Ramaswamy H. Sarma.

Degradation Mechanism of Soybean Protein B3 Subunit Catalyzed by Prolyl Endopeptidase from Aspergillus niger during Soy Sauce Fermentation

Soy sauce secondary precipitate formed due to the B₃ subunit seriously affects soy sauce's appearance quality. In this study, a prolyl endopeptidase (APE) from Aspergillus niger, which could degrade approximately 50% of the B₃ subunit and increase proline content by 24% in soy sauce, was isolated and identified. The results showed that APE was an acidic salt-tolerant serine protease (62 kDa), which was optimally active at 40 °C and pH 4.0, and retained more than 69% activity in 3 M NaCl solution over 10 days. As a potential substrate of APE, the B₃ subunit contains 10 proline residues. High salinity could not damage the hydrogen bonds, salt bridges, and interior hydrophobicity of APE; thus, the spatial structures and activity of APE in 3 M NaCl solution were stable within 3 days and decreased thereafter. High salinity made the B₃ subunit more rigid and lowered the catalytic activity of APE on the B₃ subunit, hindering complete hydrolysis of the B₃ subunit. This was the first report about the APE capable of degrading the B₃ subunit and reducing the secondary precipitate of soy sauce, providing a new possibility to solve the secondary precipitate of soy sauce.

Purification, characterization and the use of recombinant prolyl oligopeptidase from Myxococcus xanthus for gluten hydrolysis

Prolyl oligopeptidase (POP, EC 3.4.21.26) is a cytosolic serine protease that hydrolyses proline containing small peptides. The members of prolyl oligopeptidase family play important roles in many physiological processes such as neurodegenerative diseases, maturation and degradation of peptide hormones. Thus the enzyme has been purified and characterized from various sources to elucidate the potential use as therapeutics. In this study recombinant Myxococcus xanthus prolyl oligopeptidase expressed in E. coli was purified 60.3 fold, using metal-chelate affinity and gel permeation chromatography. The recombinant enzyme had a monomeric molecular weight of 70 kDa. Isoelectric point of the enzyme was found to be approximately 6.3 by two-dimensional polyacrylamide gel electrophoresis. The optimum pH and temperature was estimated as 7.5 and 37 °C, respectively. The purified enzyme was stable in a pH range of 6.0-8.5 and thermally stable up to 37 °C. The K_m and V_max values were 0.2 mM and 3.42 μmol/min/mg. The proteolytic activity was inhibited by active-site inhibitors of serine protease, Z-Pro-Prolinal, PMSF, and metal ions, Cd²⁺, and Hg²⁺. Furthermore, the hydrolysis efficiency of the recombinant prolyl oligopeptidase was investigated with wheat gluten.