Impact of macromolecular crowding on structure and properties of pepsin and trypsin

Intestinal delivery of encapsulated bacteriocin peptides in cross-linked alginate microcapsules

Oral delivery of larger bioactive peptides (>20 amino acids) to the small intestine remains a challenge due to their sensitivity to proteolytic degradation and chemical denaturation during gastrointestinal transit. In this study, we investigated the capacity of crosslinked alginate microcapsules (CLAMs) formed by spray drying to protect Plantaricin EF (PlnEF) (C-EF) in gastric conditions and to dissolve and release PlnEF in the small intestine. PlnEF is an unmodified, two-peptide (PlnE: 33 amino acids; PlnF: 34 amino acids) bacteriocin produced by Lactiplantibacillus plantarum with antimicrobial and gut barrier protective properties. After 2 h incubation in simulated gastric fluid (SGF) (pH 1.5), 43.39 % ± 8.27 % intact PlnEF was liberated from the CLAMs encapsulates, as determined by an antimicrobial activity assay. Transfer of the undissolved fraction to simulated intestinal fluid (SIF) (pH 7) for another 2 h incubation resulted in an additional release of 16.13 % ± 4.33 %. No active PlnEF was found during SGF or sequential SIF incubations when pepsin (2,000 U/ml) was added to the SGF. To test PlnEF release in C-EF contained in a food matrix, C-EF was mixed in peanut butter (PB) (0.15 g C-EF in 1.5 g PB). A total of 12.52 % ± 9.09 % active PlnEF was detected after incubation of PB + C-EF in SGF without pepsin, whereas no activity was found when pepsin was included. Transfer of the remaining PB + C-EF fractions to SIF yielded the recovery of 46.67 % ± 13.09 % and 39.42 % ± 11.53 % active PlnEF in the SIF following exposure to SGF and to SGF with pepsin, respectively. Upon accounting for the undissolved fraction after SIF incubation, PlnEF was fully protected in the CLAMs-PB mixture and there was not a significant reduction in active PlnEF when pepsin was present. These results show that CLAMs alone do not guard PlnEF bacteriocin peptides from gastric conditions, however, mixing them in PB protected against proteolysis and improved intestinal release.

Deeper Insights into Mixed Crowding through Enzyme Activity, Dynamics, and Crowder Diffusion

Given the fact that the cellular interior is crowded by many different kinds of macromolecules, it is important that in vitro studies be carried out in the presence of mixed crowder systems. In this regard, we have used binary crowders formed by the combination of some of the commonly used crowding agents, namely, Ficoll 70, Dextran 70, Dextran 40, and PEG 8000 (PEG 8), to study how these affect enzyme activity, dynamics, and crowder diffusion. The enzyme chosen is AK3L1, an isoform of adenylate kinase. To investigate its dynamics, we have carried out three single point mutations (A74C, A132C, and A209C) with the cysteine residues being labeled with a coumarin-based solvatochromic probe [CPM: (7-diethylamino-3-(4-maleimido-phenyl)-4-methylcoumarin)]. Both enzyme activity and dynamics decreased in the binary mixtures as compared with the sum of the individual crowders, suggesting a reduction in excluded volume (in the mixture). To gain deeper insights into the binary mixtures, fluorescence correlation spectroscopy studies were carried out using fluorescein isothiocyanate-labeled Dextran 70 and tetramethylrhodamine-labeled AK3L1 as the diffusion probes. Diffusion in binary mixtures was observed to be much more constrained (relative to the sum of the individual crowders) for the labeled enzyme as compared to the labeled crowder showing different environments being faced by the two species. This was further confirmed during imaging of the phase-separated droplets formed in the binary mixtures having PEG as one of the crowding agents. The interior of these droplets was found to be rich in crowders and densely packed, as shown by confocal and digital holographic microscopy images, with the enzymes predominantly residing outside these droplets, that is, in the relatively less crowded regions. Taken together, our data provide important insights into various aspects of the simplest form of mixed crowding, that is, composed of just two components, and also hint at the enhanced complexity that the cellular interior presents toward having a detailed and comprehensive understanding of the same.

Concentration Dependence of Elastic and Viscoelastic Properties of Aqueous Solutions of Ficoll and Bovine Serum Albumin by Brillouin Light Scattering Spectroscopy

The cellular environment is crowded with macromolecules of different shapes and sizes. The effect of this macromolecular crowding has been studied in a variety of synthetic crowding environments: two popular examples are the compact colloid-like Ficoll macromolecule and the globular protein bovine serum albumin (BSA). Recent studies have indicated that a significant component of bound or surface-associated water in these crowders reduces the available free volume. In this work, Brillouin light scattering experiments were performed on aqueous solutions of Ficoll 70 and Ficoll 400 with concentrations ranging from 1 to 35 wt % and BSA with concentrations of 1 to 27 wt %. From the dependence of spectral peak parameters on polymer concentration, we determined fundamental solution properties: hypersound velocity, adiabatic bulk modulus and compressibility, apparent viscosity, and hypersound attenuation. The existing theory that ignores intermolecular interactions can capture only the observed linear trends in the frequency shift up to a threshold concentration, beyond which a quadratic term accounting for intermolecular interactions is necessary. This likely indicates a transition from the dilute to semidilute regime. In the Ficoll solutions (but not BSA), we see evidence for a central mode, which is indicative of relaxation in the hydration shell of Ficoll.

Effects of combined binding of chlorogenic acid/caffeic acid and gallic acid to trypsin on their synergistic antioxidant activity, enzyme activity and stability

The combined application of multiple natural polyphenols in functional foods may provide better health benefits. The binding of polyphenols with different structures to proteins will affect their respective functions. Spectroscopy and molecular docking were used to investigate the competitive binding of chlorogenic acid (CGA)/caffeic acid (CA) and gallic acid (GA) to trypsin. The effects of different molecular structures and the order of adding the three phenolic acids on the binding were assessed. The stability of trypsin and its docked complexes with CGA/CA/GA was evaluated by molecular dynamics simulation. The effects of the binding process on the activity and thermal stability of trypsin, as well as on the antioxidant activity and stability of CGA/CA/GA were explored. The competitive binding of CGA/CA and GA to trypsin affected their synergistic antioxidant effects. The results may provide a reference for the combined application of CGA/CA and GA in food and pharmaceutical fields.

A reversibly gated protein-transporting membrane channel made of DNA

Controlled transport of biomolecules across lipid bilayer membranes is of profound significance in biological processes. In cells, cargo exchange is mediated by dedicated channels that respond to triggers, undergo a nanomechanical change to reversibly open, and thus regulate cargo flux. Replicating these processes with simple yet programmable chemical means is of fundamental scientific interest. Artificial systems that go beyond nature's remit in transport control and cargo are also of considerable interest for biotechnological applications but challenging to build. Here, we describe a synthetic channel that allows precisely timed, stimulus-controlled transport of folded and functional proteins across bilayer membranes. The channel is made via DNA nanotechnology design principles and features a 416 nm2 opening cross-section and a nanomechanical lid which can be controllably closed and re-opened via a lock-and-key mechanism. We envision that the functional DNA device may be used in highly sensitive biosensing, drug delivery of proteins, and the creation of artificial cell networks.

Interaction between Caffeic Acid Phenethyl Ester (CAPE) and Protease: Monitoring by Spectroscopic and Molecular Docking Approaches

The interaction of one anticancer drug (caffeic acid phenethyl ester, CAPE) with three proteases (trypsin, pepsin and α-chymotrypsin) has been investigated with multispectral methods and molecular docking. As an active components in propolis, the findings are of great benefit to metabolism, design and stuctural modification of drugs. The results show that CAPE has an obvious ability to quench the trypsin, pepsin, or α-chymotrypsin fluorescence mainly through a static quenching procedure. Trypsin has the largest binding affinity to CAPE, and α-chymotrypsin has the smallest binding affinity to CAPE. The data obtained from thermodynamic parameters and molecular docking prove that the spontaneously interaction between CAPE and each protease is mainly due to a combination of Van der Waals (vdW) force and hydrogen bond (H-bond), controlled by enthalpy-driven process. The binding force, strength, position, and the number of H-bond are further obtained from the results of molecular docking. Through ultraviolet spectroscopy, dynamic light scattering (DLS) and circular dichroism (CD) experiments, the change in the protease secondary structure induced by CAPE was observed. Additionally, the addition of protease had a positive impact on the antioxidative activity of CAPE, and α-chymotrypsin has the greatest impact on the removal of DPPH free radicals by CAPE.

Understanding enzyme behavior in a crowded scenario through modulation in activity, conformation and dynamics

Macromolecular crowding, inside the physiological interior, modulates the energy landscape of biological macromolecules in multiple ways. Amongst these, enzymes occupy a special place and hence understanding the function of the same in the crowded interior is of utmost importance. In this study, we have investigated the manner in which the multidomain enzyme, AK3L1 (PDB ID: 1ZD8), an isoform of adenylate kinase, has its features affected in presence of commonly used crowders (PEG 8, Dextran 40, Dextran 70, and Ficoll 70). Michaelis Menten plots reveal that the crowders in general enhance the activity of the enzyme, with the K_m and V_max values showing significant variations. Ficoll 70, induced the maximum activity for AK3L1 at 100 g/L, beyond which the activity reduced. Ensemble FRET studies were performed to provide insights into the relative domain (LID and CORE) displacements in presence of the crowders. Solvation studies reveal that the protein matrix surrounding the probe CPM (7-diethylamino-3-(4-maleimido-phenyl)-4-methylcoumarin) gets restricted in presence of the crowders, with Ficoll 70 providing the maximum rigidity, the same being linked to the decrease in the activity of the enzyme. Through our multipronged approach, we have observed a distinct correlation between domain displacement, enzyme activity and associated dynamics. Thus, keeping in mind the complex nature of enzyme activity and the surrounding bath of dense soup that the biological entity remains immersed in, indeed more such approaches need to be undertaken to have a better grasp of the "enzymes in the crowd".

Effects of macromolecular crowding on the folding and aggregation of glycosylated MUC5AC

OBJECTIVE

To investigate the effects of macromolecular crowding on the folding and aggregation of MUC5AC with different levels of glycosylation during refolding.

METHODS

Part 1:An in vitro catalytic reaction comprising the ppGalNAc T2 enzyme, uridine-5'-diphospho-N-galactosamine (UDP-GalNAc) and an 11-amino acid peptide substrate, was used to assess the enzyme activity of the ppGalNAc T2 enzyme in macromolecular crowding environment respectively with bovine serum albumin (BSA), polyethylene glycol (PEG2000), Dextran70 and Ficoll70 at different concentration and temperature. Part 2: The recombinant MUC5AC was expressed in HEK293 cells and purified by nickel column chromatography. The purified protein was treated with PNGase F, and the degree of glycosylation was analyzed by SDS-PAGE. Macromolecular crowding was simulated using PEG2000 at the concentrations of 50, 100, and 200 g/L. Deglycosylated-MUC5AC (d-MUC5AC) and glycosylated MUC5AC (g-MUC5AC) were denatured by GdnHCl and renatured by dilution in a refolding buffer. Protein aggregation was monitored continuously by absorbance reading at 488 nm using a UV spectrophotometer at 25 °C. The refolded proteins were centrifuged, the protein concentration of the supernatant was measured, and refolding yield in different refolding buffers was determined.

RESULTS

Enzyme activityof ppGalNAc T2 was observed to increase with increasing crowding agent concentration, with highest enzyme activity at 200 g/L. Compared with the group in the absence of crowding reagent, the refolding yield of g-MUC5AC and d-MUC5AC were reduced significantly in the presence of different concentrations of PEG2000 (200, 100, and 50 g/L). Compared with the dilute solution, aggregation increased significantly in the presence of PEG2000, especially at 200 g/L. Moreover, in the crowded reagent with the same concentration, the refolding yield of d-MUC5AC was higher than that of g-MUC5AC, whereas the degree of aggregation of d-MUC5AC was lower than that of g-MUC5AC.

CONCLUSION

The crowded intracellular environment reduces the refolding rate of MUC5AC and strongly induces the misfolding and aggregation of glycosylated MUC5AC.

Pepsin and Laryngeal and Hypopharyngeal Carcinomas

Laryngeal and hypopharyngeal carcinomas are common malignant tumors of the head and neck, and the incidence of both is increasing. Laryngopharyngeal reflux refers to the retrograde flow of gastric contents into the larynx, oropharynx, and/or nasopharynx. It remains controversial whether laryngopharyngeal reflux is a risk factor for laryngeal and hypopharyngeal cancers. The refluxing substances mainly include hydrochloric acid, pepsin, and occasionally bile acids and bile salts, as well as bacteria that colonize the gastrointestinal tract. Loss of epithelium in the mucous membrane of the larynx and hypopharynx is thought to be caused by pepsin. Here, we review the relationships between laryngopharyngeal reflux and both laryngeal and hypopharyngeal carcinomas, as well as the significance of pepsin, methods of clinical detection, and the mechanism of carcinogenesis.

Relationship Between Pepsin Expression and Dysplasia Grade in Patients With Vocal Cord Leukoplakia

OBJECTIVE

To measure pepsin expression in patients with vocal fold leukoplakia and elucidate its clinical significance.

STUDY DESIGN

Retrospective analysis of pathologic archive specimens.

SETTING

Affiliated university hospital.

SUBJECTS AND METHODS

The study included 45 patients with vocal fold leukoplakia and 19 with vocal fold polyps who underwent surgical treatment between December 2013 and July 2016. Masses were detected on both vocal cords in 5 patients with vocal fold leukoplakia and in 1 patient with vocal fold polyps. Immunohistochemistry was used to assess pepsin expression. In addition, the relationship of pepsin expression level with clinical characteristics of vocal fold leukoplakia was assessed.

RESULTS

The rate of pepsin expression was high in the polyp group (75%) and the leukoplakia group (68%); however, the difference between groups was not significant (P > .05). Pepsin expression significantly increased according to grade of dysplasia (mild, 57.1%; moderate, 88.9%; severe, 100.0%; P = .034). Similarly, the percentage of lesions that exhibited strongly positive pepsin expression increased with the grade of dysplasia (mild, 37.1%; moderate, 66.7%; severe, 100.0%; P = .005). The leukoplakia recurrence rate was higher in patients with positive pepsin expression than in patients with negative pepsin expression but without a significant difference (P > .05).

CONCLUSION

Our study suggests that pepsin was associated with the grade of dysplasia of vocal cord leukoplakia. Further investigation with appropriate control groups and controlling for other risk factors, such as smoking or alcohol consumption, is needed.

Natural Macromolecules as Carriers for Essential Oils: From Extraction to Biomedical Application

Essential oils (EOs) and their main constituents, the terpenes, are widely studied, mostly relating to their antioxidant ability and bioactivity, such as antimicrobial, anticancer, anti-inflammatory, and range of other actions in the living systems. However, there is limited information on their bioavailability, especially upon clinical studies. Having in mind both strong biological effects and health benefits of EOs and their specific physicochemical properties (volatility, lipophilic character, low water solubility or insolubility, viscosity, expressed odor, concentration-dependent toxicity, etc.), there is a need for their encapsulation for target delivery. Encapsulation of EOs and their constituents is the prerequisite for enhancing their oxidative stability, thermostability, photostability, shelf life, and biological activity. We considered various carrier types such a (1) monophase and polyphase polysaccharide hydrogel carriers, (2) polysaccharide-protein carriers, and (3) lipid carriers in the context of physicochemical and engineering factors. Physicochemical factors are encapsulation efficiency, chemical stability under gastric conditions, mechanical stability, and thermal stability of carrier matrices. Choice of carrier material also determines the encapsulation technique. Consequently, the engineering factors are related to the advantage and disadvantage of various encapsulation techniques frequently used in the literature. In addition, it was intended to address the interactions between (1) main carrier components, such as polysaccharides, proteins, and lipids themselves (in order to form chemically and mechanically stable structure); (2) main carrier components with pepsin under gastric conditions (in order to form resistant material under gastric conditions); and (3) main carrier components with EOs (in order to enhance encapsulation efficiency), as a necessary precondition for whole process optimization. Finally, different sources for obtaining natural carrier macromolecules are surveyed, especially the agro-waste materials and agricultural and food by-products. This review article highlights the bioavailability aspects of encapsulated EOs and physicochemical and engineering factors concerning natural macromolecule carriers for their target delivery and application.

Study of the complex coacervation mechanism between ovalbumin and the strong polyanion PSSNa: influence of temperature and pH

We studied the complex between ovalbumin and long flexible poly-(sodium 4-styrene sulfonate) as a function of pH and temperature. We used various techniques [turbidimetry, conductometry, dynamic light scattering, viscosimetry, and ultra-small-angle light scattering (USALS)] to fully characterize the coacervate complex. Different phases of complexation versus temperature were determined by turbidimetric analysis (pH_c, pH_ϕ1, and pH_ϕ2). The optimal protein/polyelectrolyte interaction occurred at pH_opt 4. An increase in temperature made the hydrophobic interactions more favorable in the case of the soluble complex and complex coacervation phases (pH > pH_ϕ2). We systematically determined the activation energy to follow the conformational changes of the complex at different temperatures. At pH_opt, the size of the formed complex showed a remarkable decrease with temperature increase. USALS was used to determine simultaneously the radius of gyration (R_g) and fractal dimension D_f of the coacervate.

Study of the complex coacervation mechanism between the lysing enzyme from T. harzianum and polyallylamine hydrochloride

Complex coacervation was achieved by mixing the lysing enzyme from T. harzianum (LYS) with polyallylamine hydrochloride (PAH). We show in this work that the study electrostatic complexes conformation can lead to the formation of dense complexes. We systematically investigated the effects of pH and the mass ratio on the structure and properties of the complex. The different transition phases (pHc, pHφ1, and pHφ2) have been determined using dynamic light scattering, zeta potential and turbidimetric measurements. The interpolymeric bonds may be ionic or physical, depending on the pH of the system. For a pH value of 4.9, the mixture system [LYS]/[PAH] gives raise the formation of coacervate droplets. The effects of temperature on the structure of coacervate droplets are studied by small angle light scattering (SALS).

Sugar osmolytes-induced stabilization of RNase A in macromolecular crowded cellular environment

Organisms synthesize sugar osmolytes during environmental stresses to protect proteins against denaturation. These studies were carried out in dilute buffer whereas intracellular milieu within cells has cytoplasmic concentration of macromolecules in the range of 80-400 mg ml^-1. Is the stabilizing effect of sugar osmolytes on the protein in dilute buffer different from that when protein is in cellular environment? To answer this question, we have measured and analysed the effect of sugar osmolytes on the structural and thermodynamic stability of ribonuclease A in the presence of dextran 70 at multiple concentrations of six sugars at different pH values. It was found that (i) each sugar osmolyte in the crowded environment provides stability to the protein in terms of T_m (midpoint of denaturation) and ∆G_D° (Gibbs energy change) and this stabilizing effect is under entropic control, (ii) the extent of osmolyte-induced stabilization of RNase A is pH dependent, and (iii) effect of sugars on the stability of protein in presence of the crowding agent remains unchanged. This study concludes that crowding does not affect the efficacy of osmolytes and vice versa; and emphasizes on understanding of internal architecture of the cellular environment with respect to molecular and macromolecular crowding.

Process-induced cell wall permeability modulates the in vitro starch digestion kinetics of common bean cotyledon cells

Cell wall barrier role during in vitro simulated digestion of starch in common bean cotyledon cells can be modified through variation of thermal processing intensity.