Buried Hydrophobic Residues Research Articles

Elucidating the microscopic origin of observed anti-correlation between the protein-protein and protein-water interaction energies

Water as a solvent plays an important role in dictating the structure and dynamics of the large biomolecules like proteins. It has been proposed that the protein dynamics and energetics are closely coupled to the water molecules in the hydration shell. In particular, it has been shown earlier that the fluctuations in intra-protein (protein-protein) interaction energy is strongly anti-correlated with the protein-water interaction energy (solvation energy). Moreover, the dynamical signatures of water gets reflected into the protein dynamics in terms of a dominant power law behavior. In this work, we have carried out systematic molecular dynamics (MD) simulations of three different protein systems to understand the key physical factors that contribute to such anti-correlations. First, we compare the dynamics in globular folded proteins like Lysozyme with intrinsically disordered peptides (IDPs) like Amyloid beta to show that enhanced conformational fluctuations lead to significantly stronger anti-correlation. Trp-cage miniprotein shows a similar behavior distributed over two sub-ensembles of folded and unfolded states. We also investigate what type of interactions and molecular processes are responsible for the observed anti-correlation. In particular, we observe that the extent of correlation decreases significantly in the order of charged, polar and non-polar amino acid residues. Charged residues that form salt bridge interactions show a dominant anti-correlation. Surprisingly, a few non-polar (hydrophobic and buried) residues demonstrate significant anti-correlation as well. We attribute this to the structural fluctuations that lead to an equilibrium between buried and solvent exposed states of these residues, where the protein-protein and protein-water interactions compensate each other. Our studies indicate that the molecular origin of the observed anti-correlation can be vary depending on the type of the interaction. The overall coupling/correlation is dominated by the electrostatic interactions and charged residues due to a general dielectric screening effect, whereas a few buried hydrophobic residues may also show such coupling due to structural dynamics between buried and exposed states.

Influence of linoleic acid on the immunodetection of shrimp (Litopenaeus vannamei) tropomyosin and the mechanism investigation via multi-spectroscopic and molecular modeling techniques

The effect of linoleic acid (LA) on the IgG/IgE recognition, in vitro digestibility and immunodetection of shrimp tropomyosin (TM) was investigated. Subsequently, the simultaneous binding of LA-TM was explored using multi-spectroscopic and molecular modeling techniques. Our findings reveled that the addition of LA significantly reduced TM’s IgG/IgE immunoreactivity, digestibility, and immunodetection. Further analysis using multi-spectroscopic and molecular modeling techniques indicated that while TM’s secondary structure remained largely unchanged, its 3-D structure showed significant alterations such as increased particle size and hydrophobic surface area, and a higher number of buried hydrophobic residues exposed due to the binding of LA to TM. These structural changes rendered it difficult for target antibodies and digestive enzymes to interact with related epitopes and cleavage sites buried inside the molecule. The results obtained in this study provide valuable insights into the molecular mechanism of poor immunodetection caused by food matrix interference.

Two sequence- and two structure-based ML models have learned different aspects of protein biochemistry

Deep learning models are seeing increased use as methods to predict mutational effects or allowed mutations in proteins. The models commonly used for these purposes include large language models (LLMs) and 3D Convolutional Neural Networks (CNNs). These two model types have very different architectures and are commonly trained on different representations of proteins. LLMs make use of the transformer architecture and are trained purely on protein sequences whereas 3D CNNs are trained on voxelized representations of local protein structure. While comparable overall prediction accuracies have been reported for both types of models, it is not known to what extent these models make comparable specific predictions and/or generalize protein biochemistry in similar ways. Here, we perform a systematic comparison of two LLMs and two structure-based models (CNNs) and show that the different model types have distinct strengths and weaknesses. The overall prediction accuracies are largely uncorrelated between the sequence- and structure-based models. Overall, the two structure-based models are better at predicting buried aliphatic and hydrophobic residues whereas the two LLMs are better at predicting solvent-exposed polar and charged amino acids. Finally, we find that a combined model that takes the individual model predictions as input can leverage these individual model strengths and results in significantly improved overall prediction accuracy.

Structural Features of Antibody-Peptide Recognition.

Antibody recognition of antigens is a critical element of adaptive immunity. One key class of antibody-antigen complexes is comprised of antibodies targeting linear epitopes of proteins, which in some cases are conserved elements of viruses and pathogens of relevance for vaccine design and immunotherapy. Here we report a detailed analysis of the structural and interface features of this class of complexes, based on a set of nearly 200 nonredundant high resolution antibody-peptide complex structures that were assembled from the Protein Data Bank. We found that antibody-bound peptides adopt a broad range of conformations, often displaying limited secondary structure, and that the same peptide sequence bound by different antibodies can in many cases exhibit varying conformations. Propensities of contacts with antibody loops and extent of antibody binding conformational changes were found to be broadly similar to those for antibodies in complex with larger protein antigens. However, antibody-peptide interfaces showed lower buried surface areas and fewer hydrogen bonds than antibody-protein antigen complexes, while calculated binding energy per buried interface area was found to be higher on average for antibody-peptide interfaces, likely due in part to a greater proportion of buried hydrophobic residues and higher shape complementarity. This dataset and these observations can be of use for future studies focused on this class of interactions, including predictive computational modeling efforts and the design of antibodies or epitope-based vaccine immunogens.

Conformational changes of tyrosinase caused by pentagalloylglucose binding: Implications for inhibitory effect and underlying mechanism

Tyrosinase is a critical enzyme related to various pigmentation disorders and browning of fruits and vegetables. In this study, a novel inhibitor pentagalloylglucose (PGG) against tyrosinase was prepared from tannic acid with the chemical structure elucidated using HPLC, ESI-MS, 1H- and 13C NMR. Its inhibitory effect and the underlying mechanism on tyrosinase were explored by enzyme kinetics, UV-scanning, copper-ion chelation, fluorescence, circular dichroism, fourier transform infrared spectroscopy and molecular docking simulation. Results revealed that the yield of PGG reached 18.0% and the purity was up to 99.09%. PGG was a high-potential inhibitor of tyrosinase with IC50 values of (15.54 ± 0.56) × 10-6 and (50.89 ± 3.34) × 10-6 mol/L for monophenolase and diphenolase, respectively. PGG could disturb the formation of dopachrome and had strong capacity to chelate copper ions. The fluorescence of tyrosinase was efficiently quenched by PGG through a static mechanism. The binding of PGG to tyrosinase was a spontaneous exothermic process that induced unfolding of the tyrosinase structure to expose more buried hydrophobic residues. Docking results implied that PGG interacted with tyrosinase by forming hydrogen bonds with amino acid residues Glu-173, Glu-208, Lys-158, Lys-180, Gln-44 and Gln-159. This study would enhance our understanding of the inhibitory mechanism of PGG on tyrosinase at the molecular level and provide scientific guidance for the application of PGG in food and pharmaceutical industries.

Nanomaterial Functionalization Modulates Hard Protein Corona Formation: Atomistic Simulations Applied to Graphitic Materials

AbstractThe protein corona is an obstacle to exploiting exotic properties of nanomaterials in clinical and biotechnological settings. The atomic‐scale dynamic formation of the protein corona at the bio‐nano interface is impenetrable using conventional experimental techniques. Here, molecular dynamics simulations are used to study the effect of graphene‐oxide (GO) functionalization on apolipoprotein‐cIII (apo‐c3) adsorption. An analysis pipeline is developed, encompassing binding energy calculations to protein structure analyses employing uniform manifold approximation and projection (UMAP) dimensionality reduction and clustering. It is found that apo‐c3 is denatured by GO adsorption, driven by the large energetic contributions of electrostatic interactions; enthalpic contributions of such binding events outweigh the intraprotein bond enthalpy required to maintain the protein tertiary structure. Through denaturing and exposing buried hydrophobic residues, the protein backbone is stabilized by forming β‐bridges, which serve as binding motifs for protein–protein interactions that drive further protein aggregation on the nanomaterial surface. In contrast, adsorption on double‐clickable azide‐ and alkyne‐double functionalized GO (C2GO), apo‐c3 largely retains its tertiary structure. Binding with the nanomaterial surface is dominated by weaker van der Waals interactions that are dispersed over the protein surface, where charged protein residues are sterically hindered by azide functional groups. The apo‐c3 C‐terminus remains unchanged upon C2GO adsorption, conserving its lipid‐binding function.

Molecular Rules Underpinning Enhanced Affinity Binding of Human T Cell Receptors Engineered for Immunotherapy

Immuno-oncology approaches that utilize T cell receptors (TCRs) are becoming highly attractive because of their potential to target virtually all cellular proteins, including cancer-specific epitopes, via the recognition of peptide-human leukocyte antigen (pHLA) complexes presented at the cell surface. However, because natural TCRs generally recognize cancer-derived pHLAs with very weak affinities, efforts have been made to enhance their binding strength, in some cases by several million-fold. In this study, we investigated the mechanisms underpinning human TCR affinity enhancement by comparing the crystal structures of engineered enhanced affinity TCRs with those of their wild-type progenitors. Additionally, we performed molecular dynamics simulations to better understand the energetic mechanisms driving the affinity enhancements. These data demonstrate that supra-physiological binding affinities can be achieved without altering native TCR-pHLA binding modes via relatively subtle modifications to the interface contacts, often driven through the addition of buried hydrophobic residues. Individual energetic components of the TCR-pHLA interaction governing affinity enhancements were distinct and highly variable for each TCR, often resulting from additive, or knock-on, effects beyond the mutated residues. This comprehensive analysis of affinity-enhanced TCRs has important implications for the future rational design of engineered TCRs as efficacious and safe drugs for cancer treatment.

Low pH-shifting treatment would improve functional properties of black turtle bean (Phaseolus vulgaris L.) protein isolate with immunoreactivity reduction.

Low pH-shifting was firstly applied in the black turtle bean (Phaseolus vulgaris L.) protein isolate treatment by acidic (pH 1.0-3.0) buffer incubation for 8h, then was adjusted to pH 7.2 and kept 3h for protein stabilizing. Mild loss of secondary structure was confirmed in the protein isolate after low pH-shifting treatment by CD and FT-IR analyses. Intrinsic fluorescence, UV spectra, surface hydrophobicity, SH content and SDS-PAGE analyses indicated the protein conformation was unfolded with the exposure of much more buried hydrophobic residues, which would result in the enhancement of emulsifying properties, foaming properties and fat holding capacity, and lead to the reduction of solubility and water holding capacity. Furthermore, lower immunoreactivity was observed by the ELISA, and improved digestibility was found in in vitro digestion assay. Our results suggested the low pH-shifting treatments would broaden the application of bean protein isolate with better hydrophobic processing functions and safety.

Promotion Effect of Succinimide on Amyloid Fibrillation of Hen Egg-White Lysozyme.

Amyloid fibrillation is closely associated with a series of neurodegenerative diseases. According to that, the intermediate soluble oligomers and protofibrils are more toxic; reducing their concentrations in protein solutions by accelerating fibrillation is believed as a feasible strategy for treatment or remission of the diseases. Using hen egg-white lysozyme (HEWL) as a model protein, the promotion effect of succinimide was revealed by a series of experiments, e.g., atomic force microscopy (AFM), thioflavin T (ThT) fluorescence assay, Far-UV circular dichroism (CD) and Raman spectroscopy, and modeling the effect of succinimide-like derivative intermediates of intramolecular deamidation of the backbone during amyloid fibrillation. The AFM measurement confirmed that succinimide effectively accelerated the morphological changes of HEWL, while at the molecular level, the accelerative transformation of protein secondary structures was also clarified by ThT fluorescence assay and Far-UV CD spectroscopy. The incubation time-dependent Raman spectroscopy further revealed that the direct transformation from α-helices to organized β-sheets occurred upon skipping the intermediate random coils under the action of succinimide. This "bridge" effect of succinimide was attributed to its special influence on disulfide bonds. In the presence of succinimide in protein solutions, the native disulfide bonds of lysozyme could be broken more efficiently and quickly within hydrolysis, resulting in exposure of the buried hydrophobic residues and accelerating the formation of cross β-sheet structures. The present investigation provides very useful information for understanding the effect of intramolecular deamidation on the whole amyloid fibrillation.

Metal binding and conformational studies of the calcium binding domain of NADPH oxidase 5 reveal its similarity and difference to calmodulin

The superoxide-generating activity of Nox5 is regulated by Ca2+ flux, primarily through its self-contained calcium binding domain (EFD). Upon Ca2+ binding, Nox5’s EFD undergoes a conformational change that exposes its buried hydrophobic residues. Previously, we determined the Ca2+ binding constants of the N-terminal half domain (N-EFD). Here we performed a similar characterization with its C-terminal lobe (C-EFD). Our studies revealed that the binding affinities (Ka’s) of the EFD are in the range of 108–105 M−1 with a strong Ca2+ binding that occurs in the C-EFD. The 3rd Ca2+ binding site also binds Mg2+ (Ka = 4.53 × 103 M−1), where its high Ca2+ binding affinity becomes moderate in cellular conditions. The essential hydrophobic exposure upon metal binding was assessed with the analysis of the 1-anilino-8-naphthalene sulfonate (ANS) interaction via fluorescence and calorimetry. While the ANS fluorescence and binding studies agree with each other in general, the results do not correlate to the actual hydrophobic exposure content. The heat capacity change (ΔCp) of Ca2+ binding for EFD is −24.1 cal/mol.K, while those of N-EFD and C-EFD are −56.3 and −41.6 cal/mol·K, respectively, indicating a significant hydrophobic exposure and polar burial. The latter was confirmed by limited trypsin digestion. The comparison of Nox5’s EFD to calmodulin, including homology modeling, was discussed in the report.Communicated by Ramaswamy H. Sarma

Thermodynamically Coupled Unfolding Transitions in Dystrophin ABD1

Dystrophin, a 427 kDa protein located on one of the largest genes in the human genome, has been implicated in myocytes’ ability to dissipate mechanical forces transduced between cytoskeletal and membrane features. Single point mutations in Dystrophin can result in myocyte membrane shearing under normal muscular flexion and is diagnosed as Becker's Muscular Dystrophy. Given point mutations outside of direct binding sites can render Dystrophin at a loss of function, the amino acids within each domain are likely stabilized or destabilized allosterically. Our research aims to determine how secondary and tertiary structures of Dystrophin can effectively couple during unfolding transitions within and between protein domains. Here, we study the actin binding domain (ABD1) of Dystrophin which contains the highest frequency of point mutations resulting in Becker's muscular dystrophy. In order to gain insight as to how ABD1 may couple within itself, we designed a series of thermodynamic analyses to describe ABD1 unfolding semi-mechanistically. We use differential scanning calorimetry as well as additional spectroscopic techniques (CD and FLT) to monitor ABD1 unfolding energetics and determine how energy may be stored in ABD1's secondary structure or in its buried hydrophobic residues. Relating these approaches provides a comparative approach as to how different structural features may affect ABD1's ability to dissipate mechanical stress through folding and unfolding thermodynamically favorable folding features.

Computational investigation of cold denaturation in the Trp-cage miniprotein

The functional native states of globular proteins become unstable at low temperatures, resulting in cold unfolding and impairment of normal biological function. Fundamental understanding of this phenomenon is essential to rationalizing the evolution of freeze-tolerant organisms and developing improved strategies for long-term preservation of biological materials. We present fully atomistic simulations of cold denaturation of an α-helical protein, the widely studied Trp-cage miniprotein. In contrast to the significant destabilization of the folded structure at high temperatures, Trp-cage cold denatures at 210 K into a compact, partially folded state; major elements of the secondary structure, including the α-helix, are conserved, but the salt bridge between aspartic acid and arginine is lost. The stability of Trp-cage's α-helix at low temperatures suggests a possible evolutionary explanation for the prevalence of such structures in antifreeze peptides produced by cold-weather species, such as Arctic char. Although the 310-helix is observed at cold conditions, its position is shifted toward Trp-cage's C-terminus. This shift is accompanied by intrusion of water into Trp-cage's interior and the hydration of buried hydrophobic residues. However, our calculations also show that the dominant contribution to the favorable energetics of low-temperature unfolding of Trp-cage comes from the hydration of hydrophilic residues.

Stability of Secondary and Tertiary Structures of Virus-Like Particles Representing Noroviruses: Effects of pH, Ionic Strength, and Temperature and Implications for Adhesion to Surfaces.

Loss of ordered molecular structure in proteins is known to increase their adhesion to surfaces. The aim of this work was to study the stability of norovirus secondary and tertiary structures and its implications for viral adhesion to fresh foods and agrifood surfaces. The pH, ionic strength, and temperature conditions studied correspond to those prevalent in the principal vehicles of viral transmission (vomit and feces) and in the food processing and handling environment (pasteurization and refrigeration). The structures of virus-like particles representing GI.1, GII.4, and feline calicivirus (FCV) were studied using circular dichroism and intrinsic UV fluorescence. The particles were remarkably stable under most of the conditions. However, heating to 65°C caused losses of β-strand structure, notably in GI.1 and FCV, while at 75°C the α-helix content of GII.4 and FCV decreased and tertiary structures unfolded in all three cases. Combining temperature with pH or ionic strength caused variable losses of structure depending on the particle type. Regardless of pH, heating to pasteurization temperatures or higher would be required to increase GII.4 and FCV adhesion, while either low or high temperatures would favor GI.1 adhesion. Regardless of temperature, increased ionic strength would increase GII.4 adhesion but would decrease GI.1 adhesion. FCV adsorption would be greater at refrigeration, pasteurization, or high temperature combined with a low salt concentration or at a higher NaCl concentration regardless of temperature. Norovirus adhesion mediated by hydrophobic interaction may depend on hydrophobic residues normally exposed on the capsid surface at pH 3, pH 8, physiological ionic strength, and low temperature, while at pasteurization temperatures it may rely more on buried hydrophobic residues exposed upon structural rearrangement.

Linoleic acid binding properties of ovalbumin nanoparticles

In the present work, ovalbumin (OVA) solutions (10g/L, 50mM NaCl, pH 7.5) were heat-treated at 75, 80 and 85°C (namely, OVA-75, OVA-80 and OVA-85, respectively), from 0 to 25min. OVA nanoparticles (OVAn) around 100nm were obtained. For 3min of heat treatment, OVAn sizes increased with temperature, but for a heating time longer than 10min, OVA-75 showed the highest size values. OVAn surface hydrophobicity increased 6–8 folds in comparison with native OVA and wavelength blue shifts of 25–30nm in maximum fluorescence intensity were registered. These results suggest that buried hydrophobic residues were exposed to the aqueous medium. Binding experiments with linoleic acid (LA) as polyunsaturated fatty acid (PUFA) model were carried out. Firstly, binding ability of OVAn was determined from LA titration curves of intrinsic fluorescence measurements. OVA-85 at 5min presented the highest binding ability and it was used for further binding properties studies (turbidity, particle size distribution – PSD – analysis and ζ-potential measurements). Turbidity measurement and PSD analysis showed that OVAn–LA nanocomplexes were formed, avoiding LA supramolecular self-assembly formation. The union of LA to OVAn surface confers them significant lower ζ-potential and larger size. Hence, fluorescence and ζ-potential results showed that LA would bind to OVAn by mean of hydrophobic interactions. Information derived from this work could be important to potentially use OVAn as PUFA vehiculization with applications in several industrial sectors (food, pharmaceutical, cosmetics, etc.).

Conjugation of Gold Nanorods with Bovine Serum Albumin Protein

We used polarized fluctuation correlation spectroscopy (p-FCS) to study the interaction of bovine serum albumin (BSA) with cetyltrimethylammonium bromide (CTAB) stabilized gold nanorods (AuNRs). The translational (DT) and rotational diffusion (DR) of the BSA-NR conjugate were determined in varying concentrations of BSA. The measured diffusion coefficients were analyzed to determine the change of the hydrodynamic size of the particle due to protein adsorption. We found that the saturation coverage is less than one monolayer of protein at a BSA concentration of ≈1 mM. The adsorption isotherm was compared with the Langmuir and anticooperative binding models to quantify BSA-NR association. Our data can be interpreted in terms of hydrophobic interaction between the imperfect CTAB coating and the buried hydrophobic residues of the protein, which results in the loss of protein native conformation. We compared our study with previous experiments involving carboxylic-acid-stabilized nanosphere interaction with BSA...

Structures of multidomain proteins adsorbed on hydrophobic interaction chromatography surfaces

In hydrophobic interaction chromatography (HIC), interactions between buried hydrophobic residues and HIC surfaces can cause conformational changes that interfere with separations and cause yield losses. This paper extends our previous investigations of protein unfolding in HIC chromatography by identifying protein structures on HIC surfaces under denaturing conditions and relating them to solution behavior. The thermal unfolding of three model multidomain proteins on three HIC surfaces of differing hydrophobicities was investigated with hydrogen exchange mass spectrometry (HXMS). The data were analyzed to obtain unfolding rates and Gibbs free energies for unfolding of adsorbed proteins. The melting temperatures of the proteins were lowered, but by different amounts, on the different surfaces. In addition, the structures of the proteins on the chromatographic surfaces were similar to the partially unfolded structures produced in the absence of a surface by temperature as well as by chemical denaturants. Finally, it was found that patterns of residue exposure to solvent on different surfaces at different temperatures can be largely superimposed. These findings suggest that protein unfolding on various HIC surfaces might be quantitatively related to protein unfolding in solution and that details of surface unfolding behavior might be generalized.

TSpred: a web server for the rational design of temperature-sensitive mutants.

Temperature sensitive (Ts) mutants of proteins provide experimentalists with a powerful and reversible way of conditionally expressing genes. The technique has been widely used in determining the role of gene and gene products in several cellular processes. Traditionally, Ts mutants are generated by random mutagenesis and then selected though laborious large-scale screening. Our web server, TSpred (http://mspc.bii.a-star.edu.sg/TSpred/), now enables users to rationally design Ts mutants for their proteins of interest. TSpred uses hydrophobicity and hydrophobic moment, deduced from primary sequence and residue depth, inferred from 3D structures to predict/identify buried hydrophobic residues. Mutating these residues leads to the creation of Ts mutants. Our method has been experimentally validated in 36 positions in six different proteins. It is an attractive proposition for Ts mutant engineering as it proposes a small number of mutations and with high precision. The accompanying web server is simple and intuitive to use and can handle proteins and protein complexes of different sizes.

Effect of limited enzymatic hydrolysis on linoleic acid binding properties of β-lactoglobulin

β-Lactoglobulin (BLG) is a member of lipocalin family, proteins with ability to bind small hydrophobic ligands, such as retinol, vitamins and fatty acids. Moreover, BLG is susceptible to protease action producing a wide range of polypeptides depending on the hydrolysis degree (HD). In the present work, the effect of limited enzymatic hydrolysis on fatty acid binding properties of BLG was studied. Linoleic acid (LA) was used as a model fatty acid. Limited enzymatic hydrolysis was performed using α-chymotrypsin immobilised on agarose microparticles. BLG hydrolysates were produced at HD: 1%, 3% and 5%. In order to determine the influence of HD on BLG molecular weight SDS–PAGE was used. BLG structural modification and LA binding properties were monitored by means of fluorescence spectroscopic techniques. The increase in HD produced: (i) a BLG degradation and a molecular weight distribution of BLG hydrolysates and (ii) an increased exposition of buried hydrophobic residues, however it was observed a decrease in surface hydrophobicity possibly due to a deterioration of hydrophobic protein domains. It was observed that enzymatic hydrolysis treatment produced a decrease in BLG ability for binding LA. It was concluded that limited enzymatic hydrolysis could deteriorate the specific site on BLG structure necessary for binding LA.

The H2A–H2B Dimeric Kinetic Intermediate Is Stabilized by Widespread Hydrophobic Burial with Few Fully Native Interactions

The H2A–H2B histone heterodimer folds via monomeric and dimeric kinetic intermediates. Within ∼5 ms, the H2A and H2B polypeptides associate in a nearly diffusion limited reaction to form a dimeric ensemble, denoted I2 and I2⁎, the latter being a subpopulation characterized by a higher content of nonnative structure (NNS). The I2 ensemble folds to the native heterodimer, N2, through an observable, first-order kinetic phase. To determine the regions of structure in the I2 ensemble, we characterized 26 Ala mutants of buried hydrophobic residues, spanning the three helices of the canonical histone folds of H2A and H2B and the H2B C-terminal helix. All but one targeted residue contributed significantly to the stability of I2, the transition state and N2; however, only residues in the hydrophobic core of the dimer interface perturbed the I2⁎ population. Destabilization of I2⁎ correlated with slower folding rates, implying that NNS is not a kinetic trap but rather accelerates folding. The pattern of Φ values indicated that residues forming intramolecular interactions in the peripheral helices contributed similar stability to I2 and N2, but residues involved in intermolecular interactions in the hydrophobic core are only partially folded in I2. These findings suggest a dimerize-then-rearrange model. Residues throughout the histone fold contribute to the stability of I2, but after the rapid dimerization reaction, the hydrophobic core of the dimer interface has few fully native interactions. In the transition state leading to N2, more native-like interactions are developed and nonnative interactions are rearranged.

Cryoprotective Effect of Sericin Enzymatic Peptides on the Freeze-Induced Denaturation of Grass Carp Surimi

In this study, cryoprotective effects of sericin enzymatic peptides (SEP) on the freeze-induced denaturation of grass carp surimi were evaluated on the basis of sulfhydryl content and surface hydrophobicity of actomyosin, as well as the SDS-PAGE pattern of myosin heavy chain (MHC) of myofibrillar proteins. Results show that SEP, containing a high polar amino acid content and abundant in amino acids with hydroxyl-containing side chain (Ser and Thr), was effective in preventing the decrease of SH content, slowing down the exposure of buried hydrophobic residues on the protein surface, and retarding the degradation of MHC in a non-linear dosage-dependent way. These findings suggest that SEP obtained in our study appear to be a promising cryoprotectant applied in the frozon storage of surimi.