Dipeptidyl peptidase IV from porcine skeletal muscle: purification and biochemical properties

Perspective of sodium reduction based on endogenous proteases via the strategy of sodium replacement in conjunction with mediated-curing

NaCl is the main curing agent in dry-cured meat products, and a large amount of NaCl addition leads to high salt content of final products. Salt content and composition are important factors affecting the activity of endogenous proteases, which in turn could affect proteolysis as well as the quality of dry-cured meat products. With the increasing emphasis on the relationship between diet and health, reducing sodium content without sacrificing quality and safety of products is a great challenge for dry-cured meat industry. In this review, the change of endogenous proteases activity during processing, the potential relationship between sodium reduction strategy, endogenous proteases activity, and quality were summarized and discussed. The results showed that sodium replacement strategy and mediated-curing had a complementary advantage in influencing endogenous proteases activity. In addition, mediated-curing had the potential to salvage the negative effects of sodium substitution by affecting endogenous proteases. Based on the results, a sodium reduction strategy that sodium replacement in conjunction with mediated-curing based on endogenous proteases was proposed for the future perspective.

Structure-based virtual screening of dipeptidyl peptidase 4 inhibitors and their in vitro analysis

Type 2 diabetes mellitus (T2DM) is one of the most widely prevalent metabolic disorders with no cure to date thus remains the most challenging task in the current drug discovery. Therefore, the only strategy to control diabetes prevalence is to develop novel efficacious therapeutics. Dipeptidyl Peptidase 4 (DPP-4) inhibitors are currently used as anti-diabetic drugs for the inhibition of incretins. This study aims to construct the chemical feature based on pharmacophore models for dipeptidyl peptidase IV. The structure-based pharmacophore modeling has been employed to evaluate new inhibitors of DPP-4. A four-featured pharmacophore model was developed from crystal structure of DPP-4 enzyme with 4-(2-aminoethyl) benzenesulfonyl fluoride in its active site via pharmacophore constructing tool of Molecular Operating Environment (MOE) consisting F1 Hyd (hydrophobic region), F2 Hyd|Cat|Don (hydrophobic cationic and donor region), F3 Acc (acceptor region) and F4 Hyd (hydrophobic region). The generated pharmacophore model was used for virtual screening of in-house compound library (the available compounds which were used for initial screening to get the few compounds for the current studies). The resultant selected compounds, after virtual screening were further validated using in vitro assay. Furthermore, structure-activity relationship was carried out for the compounds possessing significant inhibition potential after docking studies. The binding free energy of analogs was evaluated via molecular mechanics generalized Born surface area (MM-GBSA) and Poisson-Boltzmann surface area (MM-PBSA) methods using AMBER 16 as a molecular dynamics (MD) simulation package. Based on potential findings, we report that selected candidates are more likely to be used as DPP-4 inhibitors or as starting leads for the development of novel and potent DPP-4 inhibitors.

A novel and highly efficient purification procedure for native human dipeptidyl peptidase 3 from human blood cell lysate

Dipeptidyl amino-peptidase 3 (DPP3) is an aminopeptidase involved in peptide degradation, including hormone peptides as angiotensin II and enkephalins. DPP3 plasma activity increases in septic patients and correlates with mortality risk. However, the exact physiological role of DPP3 remains unclear and animal studies are necessary to reveal the function of DPP3 in vivo. To this demand, we developed a two-step purification procedure for isolation of native human DPP3 from blood cell lysate (BCL) that is suitable for in vivo applications. With the use of monoclonal antibodies coupled to beads in combination with an ion-exchange chromatography, we recovered 68% of human DPP3 activity from BCL with a purity of ≥ 95%. Purified human DPP3 was assayed for activity and protein concentration using recently published DPP3-activity- and immunoassays. Additionally, protein stability and storage in relevant buffers were tested. Our results provide a promising strategy for fast and efficient isolation of human DPP3. The purified human DPP3 represents the native state of DPP3, suitable for future in vivo applications to investigate the physiological role of DPP3 and its involvement in pathophysiological conditions.

Dipeptidyl peptidase-II from probiotic Pediococcus acidilactici: Purification and functional characterization

Dipeptidylpeptidase-II (DPP-II, E.C. 3.4.14.2), an exopeptidase was purified 15.4 fold with specific activity and yield of 15.4U/mg/mL and 14.68% respectively by a simple two step procedure from a probiotic Pediococcus acidilactici. DPP-II is 38.7KDa homodimeric serine peptidase with involvement of His and subunit mass of 18.9KDa. The enzyme exhibited optimal activity at pH 7.0 and 37°C with activation energy of 24.97kJ/mol. The enzyme retained more than 90% activity upto 50°C thus adding industrial importance. DPP-II hydrolysed Lys-Ala-4mβNA with K_M of 50μM and V_max of 30.8nmol/mL/min. In-silico characterization studies of DPP-II on the basis of peptide fragments obtained by MALDI-TOF revealed an evolutionary relationship between DPP-II of prokaryotes and phosphate binding proteins. Secondary and three-dimensional structure of enzyme was also deduced by in-silico approach. Functional studies of DPP-II by TLC and HPLC-analysis of collagen degraded products revealed that enzyme action released free amino acids and other metabolites. Microscopic and SDS-PAGE analysis of enzyme treated analysis of chicken's chest muscle (meat) hydrolysis revealed change and hydrolysis of myofibrils. This may affect the flavor and texture of meat thereby suggesting its role in meat tenderization. Being a protein of LAB (Lactic acid bacteria), it is also expected to be safe.

Intense degradation of myosin light chain isoforms in Spanish dry-cured ham

One of the main biochemical changes that take place during the processing of dry-cured ham is the degradation of the muscle protein fraction, mainly due to the action of muscle enzymes. In the present study, the isolation and tentative identification of 137 fragments from myosin light chain 1 (MLC 1), together with 88 fragments originated from myosin light chain 2 (MLC 2), have been achieved for the first time in Spanish dry-cured ham, proving the intense proteolysis experienced by myofibrillar proteins after dry-cured processing. This study was carried out by use of proteomic technology for peptide identification, and the possible enzymes contributing to the degradation of these proteins were also further discussed.

Naturally generated small peptides derived from myofibrillar proteins in Serrano dry-cured ham

A proteomic approach has been carried out to investigate the extensive proteolysis occurring in the processing of Serrano ham. In this study, a total of 14 peptide fragments derived from myosin light chain I and titin have been identified for the first time. Nine of these peptides originated from myosin light chain I protein, with the loss of dipeptides at the N-terminal position observed in some of them. This suggests that dipeptidyl peptidases are involved in the generation of dipeptides, which contribute to the generation of the characteristic taste associated with Serrano ham. The other five peptides came from the PEVK region of the titin protein. This region is believed to confer elasticity to the sarcomere as well as the ability to bind calpains. The hypothetical action of mu-calpain and calpain 3 enzymes over this region would make these enzymes potentially responsible for protein breakdown during the early dry-curing stage.