Tryptophan Fluorescence and Time-Lag Hydrolysis of Peptide Bonds during Degradation of β-Lactoglobulin by Trypsin

Modeling of the Peptide Release during Proteolysis of β-Lactoglobulin by Trypsin with Consideration of Peptide Bond Demasking

Prospects for predicting the fragmentation of polypeptide chains during their enzymatic hydrolysis using proteolysis models are considered. The opening of the protein substrate during proteolysis and the exposure of its internal peptide bonds for a successful enzymatic attack, the so-called demasking process, were taken into account. The two-step proteolysis model was used, including the parameters of demasking and the rate constants of hydrolysis of enzyme-specific peptide bonds. Herein, we have presented an algorithm for calculating the concentrations of intermediate and final peptide fragments depending on the time of hydrolysis or the degree of hydrolysis. The intermediate peptide fragments with two or one internal specific peptide bond were considered. The fragmentation of β-lactoglobulin (β-LG) by trypsin was predicted, and the calculated concentration curves for peptide fragments were compared with the experimental dependences of the concentrations on the degree of hydrolysis. Numerical parameters were proposed that characterize the concentration curves for intermediate and final peptide fragments, and they were used to compare the calculated and experimental dependences. The predicted distribution of the peptide fragments corresponded to the experimental data on the peptide release during the proteolysis of β-LG by trypsin.

Proteolysis of Micellar β-Casein by Trypsin: Secondary Structure Characterization and Kinetic Modeling at Different Enzyme Concentrations

Tryptic proteolysis of protein micelles was studied using β-casein (β-CN) as an example. Hydrolysis of specific peptide bonds in β-CN leads to the degradation and rearrangement of the original micelles and the formation of new nanoparticles from their fragments. Samples of these nanoparticles dried on a mica surface were characterized by atomic force microscopy (AFM) when the proteolytic reaction had been stopped by tryptic inhibitor or by heating. The changes in the content of β-sheets, α-helices, and hydrolysis products during proteolysis were estimated by using Fourier-transform infrared (FTIR) spectroscopy. In the current study, a simple kinetic model with three successive stages is proposed to predict the rearrangement of nanoparticles and the formation of proteolysis products, as well as changes in the secondary structure during proteolysis at various enzyme concentrations. The model determines for which steps the rate constants are proportional to the enzyme concentration, and in which intermediate nano-components the protein secondary structure is retained and in which it is reduced. The model predictions were in agreement with the FTIR results for tryptic hydrolysis of β-CN at different concentrations of the enzyme.

Modeling of Proteolysis of β-Lactoglobulin and β-Casein by Trypsin with Consideration of Secondary Masking of Intermediate Polypeptides

The opening of protein substrates during degradation by proteases and the corresponding exposure of their internal peptide bonds for a successful enzymatic attack, the so-called demasking effect, was studied for β-lactoglobulin (β-LG) and β-casein (β-CN) hydrolyzed by trypsin. Demasking was estimated by monitoring the redshift in intrinsic tryptophan fluorescence, characterizing the accessibility of polypeptide chains to aqueous medium. The secondary masking of intermediate polypeptides, giving an inverse effect to demasking, caused a restriction of the substrate opening. This led to the limitations in the red shift of fluorescence and the degree of hydrolysis with a long time of hydrolysis of β-LG and β-CN at a constant substrate concentration and reduced trypsin concentrations. The proposed proteolysis model included demasking of initially masked bonds in the protein globule or micelle, secondary masking of intermediate polypeptides, and their subsequent slow demasking. The hydrolysis of peptide bonds was modeled taking into account different hydrolysis rate constants for different peptide bonds. It was demonstrated that demasking competes with secondary masking, which is less noticeable at high trypsin concentrations. Modeling of proteolysis taking into account two demasking processes and secondary masking made it possible to simulate kinetic curves consistent with the experimental data.

Recent Advances in Biocatalysis and Metabolic Engineering

Biocatalysis refers to the utilization of enzymes, either in purified form, or existed as part of crude cell lysate or intact cells, to catalyze single- or multi-step chemical reactions, converting synthetic molecules or natural metabolites into high-value products [...]

Nanoencapsulation of lutein within lipid-based delivery systems: Characterization and comparison of zein peptide stabilized nano-emulsion, solid lipid nanoparticle, and nano-structured lipid carrier

Three lipid-based carriers encapsulating lutein, nano-emulsion (NE), solid lipid nanoparticle (SLN), and nano-structured lipid carrier (NLC), were developed from zein peptides hydrolyzed by trypsin (TZP) and flavourzyme (FZP) as stabilizers. The physiochemical properties of FZP and TZP were evaluated. The particle size, potential, microstructure, environmental stability, rheological properties, in vitro digestion stability, and bioavailability of the lutein-loaded NE, SLN, and NLC were compared. The results showed that the surface hydrophobicity of TZP was higher than that of FZP. Except for the SLN, most samples were stable against droplet aggregation during storage, and carriers stabilized by TZP exhibited more favorable storage stabilities than those prepared from FZP. All the samples presented characteristics of fluid with good fluidity. The bioavailability of lutein was between 42.61% and 62.81%. In summary, these results provide valuable insights into the design of lipid-based delivery systems for fat-soluble biologically active compounds using zein peptides as stabilizers.