Rapid Screening of Novel Dipeptidyl Peptidase-4 Inhibitory Peptides from Pea (Pisum sativum L.) Protein Using Peptidomics and Molecular Docking

Collagen derived Gly-Pro-type DPP-IV inhibitory peptides: Structure-activity relationship, inhibition kinetics and inhibition mechanism

Our previous study has demonstrated that both the amino acid at N3 position and peptide length affected the DPP-IV inhibitory activity of Gly-Pro-type peptides. To further elucidate their molecular mechanism, a combined approach of QSAR modeling, enzymatic kinetics and molecular docking was used. Results showed that the QSAR models of Gly-Pro-type tripeptides and Gly-Pro-type peptides containing 3-12 residues were successfully constructed by 5z-scale descriptor with R2 of 0.830 and 0.797, respectively. The lower values of electrophilicity, polarity, and side-chain bulk of amino acid at N3 position caused higher DPP-IV inhibitory activity of Gly-Pro-type peptides. Moreover, an appropriate increase in the length of Gly-Pro-type peptides did not change their competitive inhibition mode, but decreased their inhibition constants (Ki values) and increased interactions with DPP-IV. More importantly, the interactions between the residues at C-terminal of Gly-Pro-type peptides containing 5 ∼ 6 residues with S2 extensive subsites (Ser209, Phe357, Arg358) of DPP-IV increased the interactions of Gly residue at N1 position with the S2 subsites (Glu205, Glu206, Asn710, Arg125, Tyr662) and decreased the acylation level of DPP-IV-peptide complex, and thereby increasing peptides' DPP-IV inhibitory activity.

Enzymatic debittering of cheese flavoring and bitterness characterization of peptide mixture using sensory and peptidomics approach

Peptides in cheese flavoring produced through proteolysis plus fermentation generated bitterness. Bitterness of individual peptide can be quantified using quantitative structure-activity relationship, where molecular mass (M), hydrophobicity, residues, C-terminal hydrophobic amino acids (C-HAAs), and N-terminal basic ones (N-BAAs) are crucial. However, their accumulative influence on the overall bitterness of peptide mixture remains unknown. This study delved into extensive proteolysis to debitter and to correlate the multi-influencing factors of peptides and the collective bitterness. As hydrolysis increased from 7.5 % to 28.0 %, bitterness reduced from 5.0 to 0.3-2.7 scores, contingent on proteases used, in which FU was optimal. The overall bitterness cannot be predicted through the summation of individual peptide bitterness, which depended on M (0.5-3 kDa) and 5-23 residues, followed by N-BAAs and C-HAAs. Analysis of enzymatic cleavage sites and substrate characteristics revealed, to more effectively debitter bovine milk protein hydrolysates, proteases specifically cleaving Pro, Leu, Phe, and Val were desired.

Mechanistic Study of Novel Dipeptidyl Peptidase IV Inhibitory Peptides from Goat's Milk Based on Peptidomics and In Silico Analysis

Two novel dipeptidyl peptidase IV (DPP-IV) inhibitory peptides (YPF and LLLP) were discovered from goat milk protein by peptidomics, in silico analysis, and in vitro assessment. A total of 698 peptides (<23 AA) were successfully identified by LC-MS/MS from goat milk hydrolysates (hydrolyzed by papaian plus proteinase K). Then, 105 potential DPP-IV inhibitory peptides were screened using PeptideRanker, the ToxinPred tool, Libdock, iDPPIV-SCM, and sequence characteristics. After ADME, physicochemical property evaluation, and a literature search, 12 candidates were efficiently selected and synthesized in vitro for functional validation. Two peptides (YPF and LLLP) were found to exert relatively high in vitro chemical system (IC50 = 368.54 ± 12.97 μM and 213.99 ± 0.64 μM) and in situ (IC50 = 159.46 ± 17.40 μM and 154.96 ± 8.41 μM) DPP-IV inhibitory capacities, and their inhibitory mechanisms were further explored by molecular docking. Our study showed that the formation of strong non-bonding interactions with the core residues from the pocket of DPP-IV (such as ARG358, PHE357, GLU205, TYR662, TYR547, and TYR666) might primarily account for the DPP-IV inhibitory activity of two identified peptides. Overall, the two novel DPP-IV inhibitory peptides rapidly identified in this study can be used as functional food ingredients for the control of diabetes.

Identification, rapid screening, docking mechanism and in vitro digestion stability of novel DPP-4 inhibitory peptides from wheat gluten with ginger protease

To better understand the hypoglycemic potential of wheat gluten (WG), we screened dipeptidyl peptidase IV (DPP-4) inhibitory active peptides from WG hydrolysates. WG hydrolysates prepared by ginger protease were found to have the highest DPP-4 inhibitory activity among the five enzymatic hydrolysates, from which a 1-3 kDa fraction was isolated by ultrafiltration. Further characterization of the fraction with nano-HPLC-MS/MS revealed 1133 peptides. Among them, peptides with P'2 (the second position of the N-terminal) and P2 (the second position of the C-terminal) as proline residues (Pro) accounted for 12.44% and 43.69%, respectively. The peptides including Pro-Pro-Phe-Ser (PPFS), Ala-Pro-Phe-Gly-Leu (APFGL), and Pro-Pro-Phe-Trp (PPFW) exhibited the most potent DPP-4 inhibitory activity with IC50 values of 56.63, 79.45, and 199.82 μM, respectively. The high inhibitory activity of PPFS, APFGL, and PPFW could be mainly attributed to their interaction with the S2 pocket (Glu205 and Glu206) and the catalytic triad (Ser630 and His740) of DPP-4, which adopted competitive, mixed, and mixed inhibitory modes, respectively. After comparative analysis of PPFS, PPFW, and PPF, Ser was found to be more conducive to enhancing the DPP-4 inhibitory activity. Interestingly, peptides with P2 as Pro also exhibited good DPP-4 inhibitory activity. Meanwhile, DPP-4 inhibitory peptides from WG showed excellent stability, suggesting a potential application in type 2 diabetes (T2DM) therapy or in the food industry as functional components.

Identification and Mechanism Elucidation of Anti-Inflammatory Peptides in Jinhua Ham: An Integrative In Silico and In Vitro Study

This study aimed to effectively identify anti-inflammatory peptides in Jinhua ham, a dry-cured meat product made from the hind legs of pigs by curing and fermenting processes, and elucidate their anti-inflammatory mechanism. The investigation involved a combination of chromatographic purification, in silico screening, and in vitro validation. The first peak of JHP (JHP-P1) was purified using two-part exchange chromatography, in which 3350 peptides were identified by nano-HPLC-MS/MS, among which QLEELKR and EAEERADIAESQVNKLR showed significant anti-inflammatory potential (prediction scores: 0.759 and 0.841). In molecular docking and in vitro RAW264.7 cell experiments, these peptides displayed a strong affinity for Toll-like receptor 4-myeloid differentiation-2 (TLR4-MD-2), specifically binding around Arg 380, Lys 475, His 401, Gln 423, Asp 426, etc. This binding inhibited TLR4 expression and prevented trimer formation about TLR4-MD-2 and lipopolysaccharide (LPS), strongly inhibiting the inflammatory cascade. JHP suppressed LPS-induced cytokine overproduction and partially inhibited the phosphorylation of proteins in the MAPK/NF-κB pathway. These results demonstrated that combining in silico methods (activity prediction and molecular docking) is an effective strategy for screening anti-inflammatory peptides. This study provided a theoretical basis for identifying more anti-inflammatory peptides and applying them in functional foods.

Screening of Oral Potential Angiotensin-Converting Enzyme Inhibitory Peptides from Zizyphus jujuba Proteins Based on Gastrointestinal Digestion In Vivo

Plant proteins are a good source of active peptides, which can exert physiological effects on the body. Predicting the possible activity of plant proteins and obtaining active peptides with oral potential are challenging. In this study, the potential activity of peptides from Zizyphus jujuba proteins after in silico simulated gastrointestinal digestion was predicted using the BIOPEP-UWM™ database. The ACE-inhibitory activity needs to be further investigated. The actual peptides in mouse intestines after the oral administration of Zizyphus jujuba protein were collected and analyzed, 113 Zizyphus jujuba peptides were identified, and 3D-QSAR models of the ACE-inhibitory activity were created and validated using a training set (34 peptides) and a test set (12 peptides). Three peptides, RLPHV, TVKPGL and KALVAP, were screened using the 3D-QSAR model and were found to bind to the active sites of the ACE enzyme, and their IC50 values were determined. Their values were 6.01, 3.81, and 17.06 μM, respectively. The in vitro digestion stabilities of the RLPHV, TVKPGL, and KALVAP peptides were 82%, 90%, and 78%. This article provides an integrated method for studying bioactive peptides derived from plant proteins.

Identification of novel α-glucosidase and ACE inhibitory peptides from Douchi using peptidomics approach and molecular docking

In this study, the effect of Douchi extract (DWE) on α-glucosidase and angiotensin-converting enzymes (ACE) were investigated, and several novel peptides with inhibitory activity against α-glucosidase and ACE were identified using peptidomics approach based on UPLC-MS/MS. The average inhibition rates of DWE on α-glucosidase and ACE were 73.75-78.10% and 4.56-27.07%, respectively. In the DWE, a total of 710 peptides were detected. Two novel peptides with potential inhibitory activity against α-glucosidase were identified using the correlation analysis, database alignment and molecular docking methods. They were DVFRAIPSEVL and DRPSINGLAGAN, with the IC50 values of 0.121 and 0.128 mg/mL, respectively. Also, four novel peptides with potential inhibitory activity against ACE were identified: PSSPFTDLWD, EEQDERQFPF, PVPVPVQQAFPF and PSSPFTDL, with IC50 values of 1.388, 0.041, 0.761 and 0.097 mg/mL, respectively. These results indicated that combining peptidomics and molecular docking is an effective alternative strategy for rapidly screening numbers of novel bioactive peptides from foods.

The impacts and mechanisms of dietary proteins on glucose homeostasis and food intake: a pivotal role of gut hormones

Glucose and energy metabolism disorders are the main reasons induced type 2 diabetes (T2D) and obesity. Besides providing energy, dietary nutrients could regulate glucose homeostasis and food intake via intestinal nutrient sensing induced gut hormone secretion. However, reviews regarding intestinal protein sensing are very limited, and no accurate information is available on their underlying mechanisms. Through intestinal protein sensing, dietary proteins regulate glucose homeostasis and food intake by secreting gut hormones, such as glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY) and glucose-dependent insulinotropic polypeptide (GIP). After activating the sensory receptors, such as calcium-sensing receptor (CaSR), peptide transporter-1 (PepT1), and taste 1 receptors (T1Rs), protein digests induced Ca2+ influx and thus triggered gut hormone release. Additionally, research models used to study intestinal protein sensing have been emphasized, especially several innovative models with excellent physiological relevance, such as co-culture cell models, intestinal organoids, and gut-on-a-chips. Lastly, protein-based dietary strategies that stimulate gut hormone secretion and inhibit gut hormone degradation are proposed for regulating glucose homeostasis and food intake.

Evaluating the In Situ Insulinotropic Effects of Pea Protein Hydrolysates Mediated by Active GLP-1 via a 2D and Dual-Layered Coculture Cell Model

The aim of this study was to evaluate the in situ insulinotropic effects of pea protein hydrolysates (PPHs) mediated by active glucagon-like peptide-17-36 (active GLP-1) using a 2D and dual-layered coculture cell model. Following this model, a mixed Caco-2 and NCI-H716 cell monolayer was differentiated on the apical side to study the effects of PPHs on active GLP-1 levels; meanwhile, the beta-TC-6 cells were seeded on the basolateral side to investigate the insulin responses induced by active GLP-1. The in situ DPP-4 half-maximal inhibitory concentration (IC50) of PPHs, PPHs-120G, and PPHs-120I was 2.94, 3.43, and 2.26 mg/mL, respectively. They directly stimulated active GLP-1 secretion in NCI-H716 cells by 3.03 ± 0.21, 1.99 ± 0.03, and 2.24 ± 0.02 times, respectively. Insulin release in beta-TC-6 cells was directly stimulated by PPHs but not by PPHs-120G and PPHs-120I. Interestingly, PPHs-120G and PPHs-120I indirectly stimulated insulin release in this coculture cell model by enhancing active GLP-1 concentrations. More importantly, PPHs, PPHs-120G, and PPHs-120I increase active GLP-1 levels by their dual function of stimulating active GLP-1 secretion and DPP-4 inhibition. This study suggests that the 2D and dual-layered coculture cell model supports a more comprehensive assessment of in situ insulinotropic effects of protein hydrolysates mediated by active GLP-1.

Transepithelial Transport of the Bifunctional Peptide IPYWTY Indirectly Induced Insulin Release Mediated by Active GLP-1

There is currently no appropriate cell model suitable for evaluating the insulinotropic effects of DPP-4 inhibitory peptides (DPP-4IPs) mediated by active glucagon-like peptide-17-36 (active GLP-1). The study aims to evaluate the transepithelial transport of IPYWTY on its in situ insulinotropic effects by using a 2D and dual-layered coculture cell model that consists of Caco-2 and NCI-H716 cells on the apical (AP) side and β-TC-6 cells on the basolateral (BL) side. During transportation, IPYWTY was absorbed in its intact form through PepT1 and paracellular transport. Meanwhile, it was degraded to several peptide fragments, including PYWTY, YWTY, WTY, and IPY, which decreased its in situ DPP-4 inhibitory activity. IPYWTY does not directly stimulate insulin release in β-TC-6 cells, while it increased the active GLP-1 level from 76.57 ± 15.16 to 95.63 ± 1.99 pM (1.25 times) in NCI-H716 cells. Interestingly, IPYWTY indirectly increased insulin levels from 426.91 ± 6.07 to 573.94 ± 2.97 μIU/mL (1.34 times) in the 2D and dual-layered coculture cell model for its dual function of stimulating active GLP-1 secretion and DPP-4 inhibition. These results suggested that the 2D and dual-layered coculture cell model is an alternative strategy for effectively evaluating the insulinotropic effects of DPP-4IPs mediated by active GLP-1.