Analysis of the effect of temperature changes combined with different alkaline pH on the β-lactoglobulin trypsin hydrolysis pattern using MALDI-TOF-MS/MS

Fish oil emulsions stabilized by enzymatic hydrolysis, glycation, and fibrillation of β-Lg: Stability and EPA/DHA bioaccessibility

This study investigated the stabilization mechanism, storage stability, and in vitro digestion characteristics of oil-in-water fish oil emulsions stabilized by β-Lg modified through enzymatic hydrolysis, glycation, and fibrillation. The stabilization mechanism was elucidated by comparing droplet size, ζ-potential, interfacial protein thickness, and microstructure. Results showed that β-Lg modified through these combined processes formed a three-dimensional network, providing superior stabilization, while other modified proteins stabilized emulsions via surface adsorption. Emulsion stabilized by combined modified β-Lg maintained z-average particle sizes below 550 nm, delayed the peroxide value peak by 3 days, reduced TBARS content by 0.5 μg/mL, and remained unstratified for up to 50 days. During simulated in vitro digestion, emulsions exhibited greater stability in the gastric phase but destabilized in the intestinal phase, leading to 10.46 % higher EPA/DHA bioaccessibility than those emulsions stabilized by untreated β-Lg.

Enzymatic response of heparin-protamine complex: Spectroscopic investigation and application for lung adenocarcinoma cells detection

Though the heparin-protamine complex (HP complex) is a crucial system utilized in clinical settings, the metabolic pathways of this complex remain inadequately understood. Herein, the enzymatic degradation of the heparin-protamine complex by trypsin and its broader implications were investigated. By utilizing fluorescent gold nanoclusters liganded with the HP complex (AuNCs-HP complex), we observed significant morphological and spectral changes during enzymatic degradation. Experiments showed that AuNCs-HP complex could be degraded and cleaved into small fragments by trypsin. Moreover, the AuNCs-HP complex demonstrated its potential as a highly sensitive spectral sensing platform, enabling precise measurement of trypsin activity with an outstanding detection limit (0.34 ng mL-1). Additionally, we explored its utility for specific tumor cell detection, focusing on lung adenocarcinoma cells, and successfully identified their presence through distinctive fluorescence changes. These remarkable findings not only contribute valuable insights into targeted degradation systems but also offer promising opportunities for cancer biomarker detection. The AuNCs-HP complex serves as an innovative tool for real-time trypsin activity monitoring, paving the way for advanced biomedical applications.

Identification of New Angiotensin-Converting Enzyme Inhibitory Peptides Isolated from the Hydrolysate of the Venom of Nemopilema nomurai Jellyfish

Recently, jellyfish venom has gained attention as a promising reservoir of pharmacologically active compounds, with potential applications in new drug development. In this investigation, novel peptides, isolated from the hydrolysates of Nemopilema nomurai jellyfish venom (NnV), demonstrate potent inhibitory activities against angiotensin-converting enzyme (ACE). Proteolytic enzymes-specifically, papain and protamex-were utilized for the hydrolysis under optimized enzymatic conditions, determined by assessing the degree of hydrolysis through the ninhydrin test. Comparative analyses revealed that papain treatment exhibited a notably higher degree of NnV hydrolysis compared to protamex treatment. ACE inhibitory activity was quantified using ACE kit-WST, indicating a substantial inhibitory effect of 76.31% for the papain-digested NnV crude hydrolysate, which was validated by captopril as a positive control. The separation of the NnV-hydrolysate using DEAE sepharose weak-anion-exchange chromatography revealed nine peaks under a 0-1 M NaCl stepwise gradient, with peak no. 3 displaying the highest ACE inhibition of 96%. The further purification of peak no. 3 through ODS-C18 column reverse-phase high-performance liquid chromatography resulted in five sub-peaks (3.1, 3.2, 3.3, 3.4, and 3.5), among which 3.2 exhibited the most significant inhibitory activity of 95.74%. The subsequent analysis of the active peak (3.2) using MALDI-TOF/MS identified two peptides with distinct molecular weights of 896.48 and 1227.651. The peptide sequence determined by MS/MS analysis revealed them as IVGRPLANG and IGDEPRHQYL. The docking studies of the two ACE-inhibitory peptides for ACE molecule demonstrated a binding affinity of -51.4 ± 2.5 and -62.3 ± 3.3 using the HADDOCK scoring function.

Optimal conditions for carrying out trypsin digestions on complex proteomes: From bulk samples to single cells

To identify proteins by the bottom-up mass spectrometry workflow, enzymatic digestion is essential to break down proteins into smaller peptides amenable to both chromatographic separation and mass spectrometric analysis. Trypsin is the most extensively used protease due to its high cleavage specificity and generation of peptides with desirable positively charged N- and C-terminal amino acid residues that are amenable to reverse phase HPLC separation and MS/MS analyses. However, trypsin can yield variable digestion profiles and its protein cleavage activity is interdependent on trypsin source and quality, digestion time and temperature, pH, denaturant, trypsin and substrate concentrations, composition/complexity of the sample matrix, and other factors. There is therefore a need for a more standardized, general-purpose trypsin digestion protocol. Based on a review of the literature we delineate optimal conditions for carrying out trypsin digestions of complex proteomes from bulk samples to limiting amounts of protein extracts. Furthermore, we highlight recent developments and technological advances used in digestion protocols to quantify complex proteomes from single cells. SIGNIFICANCE: Currently, bottom-up MS-based proteomics is the method of choice for global proteome analysis. Since trypsin is the most utilized protease in bottom-up MS proteomics, delineating optimal conditions for carrying out trypsin digestions of complex proteomes in samples ranging from tissues to single cells should positively impact a broad range of biomedical research.

Simple and sensitive fluorescence detection of trypsin with Cu2+-Bovine serum albumin complex as a peroxidase mimic

Trypsin is a serine protease playing a key role in regulating pancreatic exocrine function and can be applied as a marker for the diagnosis of pancreatitis. In this work, a convenient and sensitive fluorescent assay was developed toward trypsin. Hydrogen peroxide slowly oxidized a non-fluorescent o-phenylenediamine (OPD) into a fluorescent product 2,3-diaminophenothiazine (DAP) under the catalytic from copper ions. After the introduction of bovine serum albumin (BSA), the combination of BSA with copper ions formed a peroxidase mimic and significantly accelerated the reaction rate. As an efficient protease, trypsin cleaved the lysine and arginine residues in BSA. This destroyed the binding between Cu2+ and BSA, and brought in a reduction of the catalytic effect. The accompanying decrease in fluorescence provided a response to trypsin in the range of 0.01-600 ng/mL, with a detection limit of 0.007 ng/mL. The scheme had a good selectivity and was successfully applied to the detection of real samples.

Immobilized enzyme microreactors for analysis of tryptic peptides in β-casein and β-lactoglobulin

In this study, our primary objective was to develop an effective analytical method for studying trypsin-digested peptides of two proteins commonly found in cow's milk: β-casein (βCN) and β-lactoglobulin (βLG). To achieve this, we employed two distinct approaches: traditional in-gel protein digestion and protein digestion using immobilized enzyme microreactors (μ-IMER). Both methods utilized ZipTip pipette tips filled with C18 reverse phase media for sample concentration. The μ-IMER was fabricated through a multi-step process that included preconditioning the capillary, modifying its surface, synthesizing a monolithic support, and further surface modification. Its performance was evaluated under HPLC chromatography conditions using a small-molecule trypsin substrate (BAEE). Hydrolysates from both digestion methods were analyzed using MALDI-TOF MS. Our findings indicate that the μ-IMER method demonstrated superior sequence coverage for oxidized molecules in βCN (33 ± 1.5%) and βLG (65 ± 3%) compared to classical in-gel digestion (20 ± 2% for βCN; 49 ± 2% for βLG). The use of ZipTips further improved sequence coverage in both classical in-gel digestion (26 ± 1% for βCN; 60 ± 4% for βLG) and μ-IMER (41 ± 3% for βCN; 80 ± 5% for βLG). Additionally, phosphorylations were identified. For βCN, no phosphorylation was detected using classical digestion, but the use of ZipTips showed a value of 27 ± 4%. With μ-IMER and μ-IMER-ZipTip, the values increased to 30 ± 2% and 33 ± 1%, respectively. For βLG, the use of ZipTip enabled the detection of a higher percentage of modified peptides in both classical (79 ± 2%) and μ-IMER (79 ± 4%) digestions. By providing a comprehensive comparison of traditional in-gel digestion and μ-IMER methods, this study offers valuable insights into the advantages and limitations of each approach, particularly in the context of complex biological samples. The findings set a new benchmark in protein digestion and analysis, highlighting the potential of μ-IMER systems for enhanced sequence coverage and post-translational modification detection.

Ammonia stress affects the structure and function of hemocyanin in Penaeus vannamei

Anthropogenic factors and climate change have serious effects on the aquatic ecosystem and aquaculture. Among water pollutants, ammonia has the greatest impact on aquaculture organisms such as penaeid shrimp because it makes them more susceptible to infections. In this study, we explored the effects of ammonia stress (0, 50, 100, and 150 mg/L) on the molecular structure and functions of the multifunctional respiratory protein hemocyanin (HMC) in Penaeus vannamei. While the mRNA expression of Penaeus vannamei hemocyanin (PvHMC) was up-regulated after ammonia stress, both plasma hemocyanin protein and oxyhemocyanin (OxyHMC) levels decreased. Moreover, ammonia stress changed the molecular structure of hemocyanin, modulated the expression of protein phosphatase 2 A (PP2A) and casein kinase 2α (CK2α) to regulate the phosphorylation modification of hemocyanin, and enhanced its degradation into fragments by trypsin. Under moderate ammonia stress conditions, hemocyanin also undergoes glycosylation to improve its in vitro antibacterial activity and binding with Gram-negative (Vibrio parahaemolyticus) and Gram-positive (Staphylococcus aureus) bacteria, albeit differently. The current findings indicate that P. vannamei hemocyanin undergoes adaptive molecular modifications under ammonia stress enabling the shrimp to survive and counteract the consequences of the stress.

PEGylation and antioxidant effects of a human glutathione peroxidase 1 mutant

Human glutathione peroxidase1 (hGPx1) is a good antioxidant and potential drug, but the limited availability and poor stability of hGPx1 have affected its development and application. To solve this problem, we prepared a hGPx1 mutant (GPx1M) with high activity in an Escherichia coli BL21(DE3)cys auxotrophic strain using a single protein production (SPP) system. In this study, the GPx1M was conjugated with methoxypolyethylene glycol-succinimidyl succinate (SS-mPEG, M_w = 5 kDa) chains to enhance its stability. SS-mPEG-GPx1M and GPx1M exhibited similar enzymatic activity and stability toward pH and temperature change, and in a few cases, SS-mPEG-GPx1M was discovered to widen the range of pH stability and increase the temperature stability. Lys 38 was confirmed as PEGylated site by liquid-mass spectrometry. H9c2 cardiomyoblast cells and Sprague-Dawley (SD) rats were used to evaluate the effects of GPx1M and SS-mPEG-GPx1M on preventing or alleviating adriamycin (ADR)-mediated cardiotoxicity, respectively. The results indicated that GPx1M and SS-mPEG-GPx1M had good antioxidant effects in vitro and in vivo, and the effect of SS-mPEG-GPx1M is more prominent than GPx1M in vivo. Thus, PEGylation might be a promising method for the application of GPx1M as an important antioxidant and potential drug.

Immobilization of trypsin onto porous methacrylate-based monolith for flow-through protein digestion and its potential application to chiral separation using liquid chromatography

Monolithic columns for analytical applications have attracted the researcher's attention. In this work, the laboratory-made organic-polymer monolithic column is modified with trypsin and further applied as a nanobiocatalyst microreactor and a stationary phase for separating chiral compounds by liquid chromatography. The monolith was synthesized by in-situ copolymerization of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM) as a crosslinking agent, with porogen of 1,4-butanediol/propanol/water (4:7:1 v/v) and AIBN as the radical polymerization initiator inside PEEK and silicosteel tubings (1.0 mm i.d × 100 mm) at 60 °C for 12 h. A total monomer ratio (%T) and crosslinking agent (%C) of 40:25 and 28:12 were applied to prepare poly-(GMA-co-EDMA) and poly-(GMA-co-TRIM), respectively. The produced monoliths were further modified by introducing trypsin (10 mg/L) through the ring-opening reaction of the epoxide group existing in the monolithic column. The trypsin-immobilized poly-(GMA-co-EDMA) monolithic column was applied as the nanobiocatalyst microreactor for online/flow-through and rapid digestion of β-casein sample into its peptide fragments. The trypsin-immobilized poly-(GMA-co-TRIM) column has potential application to be used as the HPLC stationary phase for the separation of R/S-citronellal enantiomers.

A proteomics approach to characterizing limited hydrolysis of whey protein concentrate

Whey Protein Concentrate was hydrolyzed by trypsin and Protease M, a novel endo/exopeptidase mix from Aspergillus oryzae. Protein peptide profiling demonstrated that Protease M preferentially hydrolyzedα-lactalbumin (α-la), while trypsin targeted β-lactoglobulin (β-lg). Peptide fractions were analyzed by liquid chromatography coupled with tandem mass-spectrometry to characterize differences in enzyme specificity, peptide hydrophobicity, and bioactivity, using bioinformatics tools. While trypsin cleaved at the C-terminal end of lysine and arginine, Protease M contributed to pepsin-like endopeptidase activity coupled with carboxyl, amino, and leucine exopeptidase activity, resulting in relatively more hydrophilic peptides compared to those released by trypsin hydrolysis. While trypsin and Protease M had varying specificity, 9 bioactive peptides were common among the hydrolysates, which was attributed to the exopeptidase activity of Protease M. The proteomics coupled with bioinformatics approach provided fundamental knowledge needed to optimize whey protein hydrolysis in a direct and efficient manner for targeted applications.

Alternative method for trypsin-based cell dissociation using poly (amino ester) coating and pH 6.0 PBS

To maintain the cellular functions of a stem cells for therapeutic tissue engineering, an advanced cell culture method for safe cell dissociation is necessary. We developed a novel cell dissociation method by applying pH-responsive bioreducible polymer on the surface of tissue culture plates (TCPs). We applied acid-responsive bioreducible poly (amino ester) (PAE) as a new candidate for surface coating method to develop alternative cell dissociation method against conventional enzyme (trypsin-ethylene diamine tetra acetic acid (EDTA)) treatment. Human adipose derived stem cells (hADSCs) were cultured on and dissociated from PAE-coated TCPs to compare cell adhesion, cell proliferation, cell viability, and functionality to those of the cells cultured on and dissociated with trypsin-EDTA from normal TCPs without PAE coating. To confirm the in vivo therapeutic efficacy of the hADSCs retrieved from PAE-coated TCPs compared to that of the cells retrieved from normal TCPs with trypsin-EDTA, we induced skin defects at the dorsal area of mice and injected the cells collected from both conditions. With the PAE coating method, cell adhesion, cell proliferation, cell viability, and functionality, especially the angiogenic efficacy, were well preserved when compared to those of the cells treated with trypsin-EDTA. In addition to in vitro results, injecting hADSCs retrieved from PAE-coated TCPs showed similar in vivo angiogenesis and wound closing efficiency compared to those of injecting hADSCs retrieved from normal TCPs with trypsin-EDTA treatment at 2 weeks after the transplantation into mouse skin wound models. We proposed the alternative method for the cell dissociation with pH-responsive bioreducible polymer, PAE. This PAE coating method may lead to the development of alternative cell dissociation method without using enzyme for future regenerative medicine and stem cell therapy.

Exploring the Use of a Modified High-Temperature, Short-Time Continuous Heat Exchanger with Extended Holding Time (HTST-EHT) for Thermal Inactivation of Trypsin Following Selective Enzymatic Hydrolysis of the β-Lactoglobulin Fraction in Whey Protein Isolate

Tryptic hydrolysis of whey protein isolate under specific incubation conditions including a relatively high enzyme:substrate (E:S) ratio of 1:10 is known to preferentially hydrolyse β-lactoglobulin (β-LG), while retaining the other major whey protein fraction, i.e., α-lactalbumin (α-LA) mainly intact. An objective of the present work was to explore the effects of reducing E:S (1:10, 1:30, 1:50, 1:100) on the selective hydrolysis of β-LG by trypsin at pH 8.5 and 25 °C in a 5% (w/v) WPI solution during incubation periods ranging from 1 to 7 h. In addition, the use of a pilot-scale continuous high-temperature, short-time (HTST) heat exchanger with an extended holding time (EHT) of 5 min as a means of inactivating trypsin to terminate hydrolysis was compared with laboratory-based acidification to <pH 3 by the addition of HCl, and batch sample heating in a water bath at 85 °C. An E:S of 1:10 resulted in 100% and 30% of β-LG and α-LA hydrolysis, respectively, after 3 h, while an E:S reduction to 1:30 and 1:50 led >90% β-LG hydrolysis after respective incubation periods of 4 and 6 h, with <5% hydrolysis of α-LA in the case of 1:50. Continuous HTST-EHT treatment was shown to be an effective inactivation process allowing for the maintenance of substrate selectivity. However, HTST-EHT heating resulted in protein aggregation, which negatively impacts the downstream recovery of intact α-LA. An optimum E:S was determined to be 1:50, with an incubation time ranging from 3 h to 7 h leading to 90% β-LG hydrolysis and minimal degradation of α-LA. Alternative batch heating by means of a water bath to inactivate trypsin caused considerable digestion of α-LA, while acidification to <pH 3.0 restricted subsequent functional applications of the protein.

Production of Antioxidant and ACEI Peptides from Cheese Whey Discarded from Mexican White Cheese Production

Cheese whey, a byproduct of the cheese-making industry, is discarded in many countries in the environment, causing pollution. This byproduct contains high-quality proteins containing encrypted biologically active peptides. The objective of this work was to evaluate the suitability of using this waste to produce bioactive peptides by enzymatic hydrolysis with a digestive enzyme. Cheese whey from white cheese (Panela cheese) was concentrated to increase total protein and hydrolyzed with trypsin. A central composite design was used to find the best conditions of pH and temperature, giving the higher antioxidant capacity and Δ Angiotensin-converting enzyme inhibition (Δ ACEI) activity. Higher biological activities were found when hydrolysis was performed at 52 °C and a pH of 8.2. The maximum value for the 2,2- diphenyl-1-picrylhydrazyl (DPPH)-scavenging activity was 26%, while the higher Δ ACE inhibition was 0.89. Significant correlations were found between these biological activities and the peptides separated by HPLC. The hydrophilic fraction (HI) showed highly significant correlations with the antioxidant capacity (r = 0.770) and with Δ ACE inhibition (r = 0.706). Antioxidant capacity showed a significant positive correlation with 34 peaks and Δ ACE inhibition with 33 peaks. The cheese whey was successfully used as raw material to produce peptides showing antioxidant capacity and ACEI activity.

Trypsin of Litopenaeus vannamei is required for the generation of hemocyanin-derived peptides

Hemocyanin is a copper containing respiratory glycoprotein in arthropods and mollusks, which also have multiple functions in vivo. Recent studies have shown that hemocyanin could generate several peptides, which play important roles in shrimp innate immunity. However, how these hemocyanin-derived peptides are generated is still largely unknown. In this study, we report for the first time that the generation of hemocyanin-derived peptides was closely correlated with trypsin expression in shrimp hepatopancreas following infection with different bacteria. RNA interference (RNAi) mediated knockdown of trypsin or treatment with the serine protease inhibitor, aprotinin, resulted in significant decrease in the levels of hemocyanin-derived peptides. Moreover, recombinant trypsin (rTrypsin) was able to hydrolyse hemocynin in vitro with the hydrolysate having a high bacterial agglutination activity while the denatured hemocynin untreated with rTrypsin lost its agglutination activity. Taken together, our current results showed that the generation of hemocyanin-derived peptides correlates with an increase trypsin expression.

Impact of the environmental conditions and substrate pre-treatment on whey protein hydrolysis: A review

Proteins in solution are subject to myriad forces stemming from interactions with each other as well as with the solvent media. The role of the environmental conditions, namely pH, temperature, ionic strength remains under-estimated yet it impacts protein conformations and consequently its interaction with, and susceptibility to, the enzyme. Enzymes, being proteins are also amenable to the environmental conditions because they are either activated or denatured depending on the choice of the conditions. Furthermore, enzyme specificity is restricted to a narrow regime of optimal conditions while opportunities outside the optimum conditions remain untapped. In addition, the composition of protein substrate (whether mixed or single purified) have been underestimated in previous studies. In addition, protein pre-treatment methods like heat denaturation prior to hydrolysis is a complex phenomenon whose progression is influenced by the environmental conditions including the presence or absence of sugars like lactose, ionic strength, purity of the protein, and the molecular structure of the mixed proteins particularly presence of free thiol groups. In this review, we revisit protein hydrolysis with a focus on the impact of the hydrolysis environment and show that preference of peptide bonds and/or one protein over another during hydrolysis is driven by the environmental conditions. Likewise, heat-denaturing is a process which is dependent on not only the environment but the presence or absence of other proteins.

Simple model of pH-induced protein denaturation

The pH-induced conformational changes of proteins are systematically studied in the framework of a hydrophobic-polar (HP) model, in which proteins are dramatically simplified as chains of hydrophobic (H) and polar (P) beads on a lattice. We express the electrostatic interaction, the principal driving force of pH-induced unfolding that is not included in the conventional HP model, as the repulsive energy term between P monomers. As a result of the exact enumeration of all of the 14- to 18-mers, it is found that lowest-energy states in many sequences change from single "native" conformations to multiple sets of "denatured" conformations with an increase in the electrostatic repulsion. The switching of the lowest-energy states occurs in quite a similar way to real proteins: it is almost always between two states, while in a small fraction of ≥16-mers it is between three states. We also calculate the structural fluctuations for all of the denatured states and find that the denatured states contain a broad range of incompletely unfolded conformations, similar to "molten globule" states referred to in acid or alkaline denatured real proteins. These results show that the proposed model provides a simple physical picture of pH-induced protein denaturation.

Mechanical properties of protein adsorption layers at the air/water and oil/water interface: a comparison in light of the thermodynamical stability of proteins

Over the last decades numerous studies on the interfacial rheological response of protein adsorption layers have been published. The comparison of these studies and the retrieval of a common parameter to compare protein interfacial activity are hampered by the fact that different boundary conditions (e.g. physico-chemical, instrumental, interfacial) were used. In the present work we review previous studies and attempt a unifying approach for the comparison between bulk protein properties and their adsorption films. Among many common food grade proteins we chose bovine serum albumin, β-lactoglobulin and lysozyme for their difference in thermodynamic stability and studied their adsorption at the air/water and limonene/water interface. In order to achieve this we have i) systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and ii) we addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions. We could show that thermodynamically less stable proteins adsorb generally faster and yield films with higher shear rheological properties at air/water interface. The same proteins showed an analog behavior when adsorbing at the limonene/water interface but at slower rates.