Changes In Protein Secondary Structure Research Articles

Microencapsulating role of whey protein isolate and sucrose in protecting the cell membrane and enhancing survival of probiotic lactobacilli strains during spray drying, storage, and simulated gastrointestinal passage

Limosilactobacillus reuteriKUB-AC5 andLactobacillus johnsoniiKUNN19-2 were spray-dried using whey protein isolate, sucrose, and whey protein isolate combined with sucrose at 130 °C and 150 °C. Differences in membrane fatty acid compositions of probiotics led to differences in cell membrane fluidity, cell injury, and cell survival during spray drying. Combination of whey protein isolate and sucrose improved survival of L. reuteriKUB-AC5, whose cell membrane were more fluid and more sensitive to stress, while whey protein isolate provided the best protection for L. johnsoniiKUNN19-2 against changes in protein secondary structures. Moreover, a relationship was found between membrane damage and the shelf-life ofmicrocapsules. Both microencapsulated cells prepared at the inlet temperature of 130 °C showed an enhanced survival upon simulated gastric digestion compared to the free cells. A thorough understanding of injury sites during spray drying will contribute to establishing optimal conditions and encapsulant formulations that maintain the cells’ viability during spray drying, storage, and gastrointestinal passage.

Biomolecular modifications in the sacfry of Mogurnda adspersa in response to copper stress

Copper (Cu) is one of the most harmful contaminants in fresh-water systems. Fish larvae such as sacfry are particularly vulnerable to metals such as copper (Cu) due to a less-developed excretory organ system and permeable skin that can absorb metals directly from the water. However, the sublethal effects of metals on this life stage are not well understood. This study assessed the sublethal toxicity of Cu on purple-spotted gudgeon sacfry (PSG, Mogurnda adspersa). For this purpose, 96h Cu toxicity bioassays were performed and toxic effects of Cu on PSG were measured at different levels of biological organization, from the individual (loss of equilibrium, wet weight), to tissue (chemical changes in retinal tissue composition) and molecular responses (whole body amino acid (AA) profiles). The EC10 and EC50 (ECx: effect concentration that affected X% of test organisms) were found to be 12 (9 - 15) µg Cu L-1 and 22 (19 - 24) µg Cu L-1, respectively. Copper stress caused a decrease in total amino acid content and changed the AA profile of PSG compared to the controls. Proton-induced X-ray emission (PIXE) mapping techniques showed accumulation of Cu in the retinal tissues disturbing the distribution of other elements such as zinc, sulfur, phosphorus and potassium. Fourier-transform infrared (FTIR) microspectroscopy of control and Cu treated eye tissues revealed a change in protein secondary structure in retinal tissues in response to Cu accumulation, as well as decreased levels of the molecular retinal, consistent with the degradation of rhodopsin, a key protein in the visual sensory system. This is the first study to demonstrate the multi-level responses of PSG arising from exposure to environmentally realistic Cu concentrations and suggests that AA profiling can serve as a useful tool to assess the impacts of metals on fresh-water organisms.

Metabolic Fingerprint Analysis of Cytochrome b 5-producing E. coli N4830-1 Using FT-IR Spectroscopy.

Optimization of recombinant protein expression in bacteria is an important task in order to increase protein yield while maintaining the structural fidelity of the product. In this study, we employ Fourier transform infrared (FT-IR) spectroscopy as a high throughput metabolic fingerprinting approach to optimize and monitor cytochrome b5 (CYT b5) production in Escherichia coli N4830-1, as the heterologous host. Cyt b5 was introduced as a plasmid with between 0 and 6 copies under a strong promoter. The FT-IR spectroscopy results combined with multivariate chemometric analysis illustrated discriminations among culture conditions as well as revealing features that correlated to the different cytb5 gene copy numbers. The second derivative of the FT-IR spectral data allowed for the quantitative detection of Cyt b5 directly inside the intact cells without the need for extraction, and highlighted changes in protein secondary structure that was directly correlated to the cytb5 gene copy number and protein content, and was in complete agreement with quantitative findings of standard traditional techniques such as SDS–PAGE and western blot analysis.

Alteration of collagen thermal denaturation, structural and the abrogation of allergenicity in eel skin induced by ohmic heating

This study aimed to evaluate the effect of ohmic heating (OH) on the thermal denaturation, structure, and allergenicity of collagen in fresh eel skin. The allergenicity of collagen decreased by approximately 70% at 50 °C as measured by simulated gastric fluid (SGF), simulated intestinal fluid (SIF) and ELISA in vitro. SDS-PAGE analysis showed that the molecular weight of collagen did not decrease, but the band strength decreased with an increase in the processing temperature. FTIR and SEM analyses showed that the secondary structure and microstructure of collagen also changed. The water retention, dielectric properties and amino acid content of collagen also decreased with increasing temperature. Compared to water bath heating (WH), OH required significantly less time and energy and reduced the allergenicity of fish skin collagen through protein unfolding and secondary structure changes, thus potentially reducing the allergenicity of eel.

Characteristics of silver carp surimi gel under high temperature (≥100 °C): quality changes, water distribution and protein pattern

AbstractThe effects of high‐temperature treatments (100–125 °C) on the properties of silver carp surimi gel were studied. The results showed that the gel strength and water holding capacity (WHC) of surimi gel decreased significantly (P < 0.05), with the increase of heating temperature and the prolongation of heating time, and the higher the temperature, the greater the decrease trend. Hydrophobic interaction and disulphide bonds decreased significantly, while ionic bonds increased significantly (P < 0.05), as well as β‐sheet increased while β‐turn and coil decreased significantly, which confirmed the changes of protein secondary structure caused by high‐temperature treatments. Myosin heavy chain (MHC) and actin bands gradually narrowed, and the production of new bands larger than 250 kDa by SDS‐PAGE showed the aggregation and cross‐linking reaction of proteins. However, the increased band intensity of 50–75 kDa and the increase of trichloroacetic acid (TCA) soluble peptides showed the degradation of proteins. The decrease of PT22 and the increase of PT23 indicated the conversion of immobilised water to free water in the gel matrix. In conclusion, high‐temperature heating caused the changes of protein secondary structure as well as chemical forces and water conversion, resulting in protein denaturation, aggregation, cross‐linking and degradation, forming a loosen and irregular gel network.

Observation of anomalous carotenoid and blind chlorophyll activations in photosystem I under synthetic membrane confinements

The role of natural thylakoid membrane confinements in architecting the robust structural and electrochemical properties of PSI is not fully understood. Most PSI studies till date extract the proteins from their natural confinements that can lead to non-native conformations. Recently our group had successfully reconstituted PSI in synthetic lipid membranes using detergent-mediated liposome solubilizations. In this study, we investigate the alterations in chlorophylls and carotenoids interactions and reorganization in PSI based on spectral property changes induced by its confinement in anionic DPhPG and zwitterionic DPhPC phospholipid membranes. To this end, we employ a combination of absorption, fluorescence, and circular dichroism (CD) spectroscopic measurements. Our results indicate unique activation and alteration of photoresponses from the PSI carotenoid (Car) bands in PSI-DPhPG proteoliposomes that can tune the Excitation Energy Transfer (EET), otherwise absent in PSI at non-native environments. Specifically, we observe broadband light harvesting via enhanced absorption in the otherwise non-absorptive green region (500–580 nm) of the Chlorophylls (Chl) along with ~64% increase in the full-width half maximum of the Qy band (650–720 nm). The CD results indicate enhanced Chl-Chl and Chl-Car interactions along with conformational changes in protein secondary structures. Such distinct changes in the Car and Chl bands are not observed in PSI confined in DPhPC. The fundamental insights into membrane microenvironments tailoring PSI subunits reorganization and interactions provide novel strategies for tuning photoexcitation processes and rational designing of biotic-abiotic interfaces in PSI-based photoelectrochemical energy conversion systems.

Design of cysteine-S-sulfonated keratin via pH driven processes: Micro-Structural Properties, biocidal activity and in vitro validation

Cysteine-S-sulfonated keratin, protein extracted from wool fibers by sulfitolysis, is a natural polyelectrolyte typically used in biomedical materials like scaffolds and smart biointerfaces. In order to extend and tune its properties, a study of the content of secondary structures, thermostability, biocidal activity and in vitro tests of cell viability on lyophilized cysteine-S-sulfonated keratin were carried out as a function of the pH solution (after keratin extraction and before purification). The results offer considerable evidence of the formation of protein–ligand complexes due to the protonation of keratin, with the presence of bisulfite, citrate, formate and acetate ions. These interactions modify the content of secondary structures in cysteine-S-sulfonated keratin, increase its thermostability (∼50 °C), enhance the stability of positive charges that confers its biocidal activity (pHsolution < 5.2) and change the interaction between cysteine-S-sulfonated keratin and human mesenchymal stem cells. Lastly, in vitro and antibacterial tests confirm that pH changes may also influence cell and bacteria response, in terms of proliferation, due to the changes of protein secondary structure and positive/negative charges. These results give relevant insights into the process of tuning keratin properties for biomedical applications – i.e., drug delivery, wound healing.

Different thermal treatments of highland barley kernel affect its flour physicochemical properties by structural modification of starch and protein

Highland barley (HB) has become popular due to nutritional benefits, and thermal treatment could broaden its application. In this study, superheated steam (SS) as a novel commercially thermal treatment was compared with other traditional heating (steam and roasting). The physiochemical properties of treated HB kernels and subsequent produced flour were investigated. After thermal treatments, gelatinization enthalpy was decreased by 38.39% and the degree of gelatinization was increased by 38.40%. SS at 180 °C (SS-180) induced the highest thermal stability, lowest viscoelasticity gel and delayed the starch retrogradation compared to other treatments. Meanwhile, SS-180 caused lowest short-range order and relative crystallinity of starch along with changes in protein secondary structure. Particularly, SS-180 decreased damaged starch content by 6.44% due to starch granules closely wrapped by glue-like protein, while steam and roasting increased it by 32.92% and 21.40%, respectively. Overall, SS treatment is most effective to improve the physiochemical properties of HB.

Protection against ulcerative colitis and colorectal cancer by evodiamine via anti‑inflammatory effects.

Evodiamine (Evo) is an alkaloid that can be extracted from the berry fruit Evodia rutaecarpa and has been reported to exert various pharmacological effects, such as antidiarrheal, antiemetic and antiulcer effects. In vivo, the potential effects of Evo were investigated in a mouse model of dextran sodium sulfate (DSS)-induced ulcerative colitis (UC) and in adenomatous polyposis coli (Apc)MinC/Gpt C57BL/6 mice with colorectal cancer (CRC), where the latter harbours a point-mutation in the Apc gene. Evo suppressed the degree of weight loss and colon shortening induced by DSS, decreased the disease activity index value and ameliorated the pathological alterations in the colon of mice with UC as examined via H&E staining of colon tissues. In addition, Evo decreased the number and size of colonic tumors in ApcMinC/Gpt mice. Proteomics (colon tissues), ELISA (colon tissues and serum) and western blotting (colon tissues) results revealed that Evo inhibited NF-κB to mediate the levels of various cytokines, including, in the DSS-induced UC model, IL-1β, IL-2, IL-6, IL-8, TNF-α, IFN-γ (ELISA of colon tissues and serum), NF-κB, IKKα+β, IκBα, S100a9, TLR4 and MyD88 (western blotting of colon tissues), and, in the colorectal cancer model, IL-1β, IL-2, IL-6, IL-15, IL-17, IL-22, TNF-α (ELISA of colon tissues and serum), NF-κB, IKKα+β, IκBα and S100a9 (western blotting of colon tissues), to achieve its anti-inflammatory and antitumor effects. In vitro, Evo also reduced the viability of the colon cancer cell line SW480, inhibited mitochondrial membrane potential (MMP detection), caused G2/M-phase arrest (cell cycle detection) and suppressed the translocation of phosphorylated-NF-κB from the cytoplasm into the nucleus (immunofluorescence of p-NF-κB). Theoretical evidence (MD simulations) suggest that Evo may bind to the ordered domain (α-helix) of NF-κB to influence this protein. The protein secondary structure changes were analyzed by the cpptraj module in Amber. In addition, these data provide experimental evidence that Evo may be an effective agent for treating UC and CRC.

Relationship between protein structure and eating quality of rice under different nitrogen application rate

AbstractBackground and ObjectivesThe mechanisms underlying the effects of proteins on the eating quality of rice remain elusive. In this study, the effect of content and secondary structure of four rice proteins (glutelin, globulin, albumin, and prolamin) on eating quality was investigated with rice subjected to nitrogen treatment at 160, 210, 260, 315, and 420 kg N/ha in the field.FindingsThe results showed that applying nitrogen fertilizer remarkably increased glutelin and globulin contents (p &lt; .05), especially the methionine content of globulin, leading to increased hardness of cooked rice. Moreover, excessive nitrogen significantly reduced the ratio of the prolamin α‐helix structure (p &lt; .05), which had a significant correlation with hardness and pasting temperature (p &lt; .05), at correlation coefficients of −0.859 and 0.828, respectively.ConclusionBesides protein content, the changes in amino acid content and protein secondary structure were also closely related to the eating quality of rice.Significance and NoveltyThose results provided a new idea for breeding, cultivating, and processing technology regulation aimed at improving the eating quality of rice.

Stability of low density lipoprotein particles affect the formation of off-flavor in thermal egg yolk

This study aimed to investigate the role of stability of low density lipoprotein (LDL) spherical particles as well as oxidation of lipids and proteins on formation of off-odor in heated egg yolk (EY). Off-odor attributes and volatile components of EY with different thermal temperature (25 °C–90 °C) were investigated by sensory evaluation, gas chromatography-mass spectrometry (GC–MS) and GC-ion mobility spectrometry (IMS). The off-flavor and volatile compounds increased significantly when EY were heated at 60 °C–65 °C. Destruction of LDL particle structure was presented by confocal laser scanning microscopy with thermal treatment at 60 °C. A positive correlation (r = 0.899, p < 0.05) was shown between oil exudation and off-odor of heated EY. Moreover, oxidation of lipids and proteins, protein aggregation, and changes of protein secondary structure (increased β-sheets and decreased α-helices) in LDL particles were all found when heating temperature rose to 65 °C. It was speculated that unstability of LDL particles resulted in the leakage of lipids; then oxidative products of lipids took part in the formation of off-odor volatiles in heated EY.

Abstract P2-08-07: Predicting DCIS prognosis using infrared and raman spectroscopy of breast calcifications and soft-tissue microstructure

Abstract Introduction: Ductal carcinoma in situ (DCIS) is a potential precursor of invasive breast cancer. The uncertain trajectory of DCIS, to progress to invasive disease or to remain in situ, currently drives treatment, despite lack of proven benefit. Therefore, understanding the molecular features of the DCIS trajectory may prevent overtreatment of this disease. Breast calcifications are a common feature in DCIS and are seen mammographically in over 80% of cases. Calcifications have been largely characterised based only on x-ray morphology; their chemical composition, their association with the surrounding soft tissue and role in DCIS and invasive breast cancer biology is largely unexplored. In this regard, a bio-photonic approach, based on infrared (IR) and Raman spectroscopy in combination with machine learning, was used to study DCIS by probing the chemical composition of calcifications and the surrounding soft tissue in breast lesions. The main aim of the work is to identify molecular compositional changes in calcifications and in soft tissue that potentially accompany or drive the progression of DCIS to invasive breast cancer, or indicates a stable DCIS phenotype. Methods: Serial tissue sections from 303 patients with (i) ‘pure DCIS’ (DCIS without recurrence) (n=158), (ii) ‘DCIS with invasive recurrence’ (DCIS from a patient who subsequently was known to develop invasive disease) (n=123) and (iii) ‘DCIS plus invasive cancer contemporaneously’ (n=22), were measured using mid-IR imaging and Raman mapping. The same calcifications and soft tissue regions from specific DCIS ducts were targeted across the techniques on the serial sections. Spectral images were analysed using cluster analysis followed by unsupervised and supervised machine learning classification models to identify spectral features associated with the progression of DCIS to invasive breast cancer. Results: Segmentation of IR and Raman spectral images based on cluster analysis identified important histopathological features including calcifications, epithelium, necrotic areas, connective tissue and stroma based on the spectral heterogeneity. Based on analysis of Raman calcification data from 145 patients with (i) ‘pure DCIS’ (n=90) and (ii) ‘DCIS with invasive recurrence’ (n=55), an area under the receiver operating characteristic (AUROC) mean value of 85% was obtained in distinguish pure DCIS from DCIS that later recurred as invasive cancer. The calcification features appeared to indicate pathology specific changes in phosphate and carbonate content and appearance of magnesium whitlockite. Similar analysis of the surrounding soft tissue spectral features showed an AUROC mean value of 76%, which showed changes in protein secondary structure and content, particularly in the necrotic regions surrounding calcifications. In addition, classification models are being developed and refined from the IR spectral data, the initial results of which have shown an AUROC value of only 54% from the same patients’ data. Perspectives: It is anticipated that the current novel approaches allowing label-free measurement of calcifications and soft tissue will provide important cues in understanding DCIS prognosis and could be a promising way forward in determining DCIS management. Current and future efforts include identification of specific discriminatory spectral features for molecular and pathological correlation. Acknowledgments: This work was supported by Cancer Research UK and by KWF Kankerbestrijding (ref. C38317/A24043). Citation Format: Jayakrupakar Nallala, Doriana Calabrese, Sarah Gosling, Allison Hall, Sarah Pinder, Ihssane Bouybayoune, Lorraine King, Jeffrey Marks, Esther Lips, Thomas Lynch, Donna Pinto, Jelle Wesseling, Shelley Hwang, Keith Rogers, Nick Stone, on behalf of the Grand Challenge PRECISION consortium. Predicting DCIS prognosis using infrared and raman spectroscopy of breast calcifications and soft-tissue microstructure [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-07.

Measurement of Secondary Structure Changes in Poly-L-lysine and Lysozyme during Acoustically Levitated Single Droplet Drying Experiments by In Situ Raman Spectroscopy.

Drying processes such as spray drying, as commonly used in the pharmaceutical industry to convert protein-based drugs into their particulate form, can lead to an irreversible loss of protein activity caused by protein secondary structure changes. Due to the nature of these processes (high droplet number, short drying time), an in situ investigation of the structural changes occurring during a real drying process is hardly possible. Therefore, an approach for the in situ investigation of the expected secondary structural changes during single droplet protein drying in an acoustic levitator by time-resolved Raman spectroscopy was developed and is demonstrated in this paper. For that purpose, a self-developed NIR–Raman sensor generates and detects the Raman signal from the levitated solution droplet. A mathematical spectral reconstruction by multiple Voigt functions is used to quantify the relative secondary structure changes occurring during the drying process. With the developed setup, it was possible to detect and quantify the relative secondary structure changes occurring during single droplet drying experiments for the two chosen model substances: poly-L-lysine, a homopolypeptide widely used as a protein mimic, and lysozyme. Throughout drying, an increase in the β-sheet structure and a decrease in the other two structural elements, α-helix, and random coil, could be identified. In addition, it was observed that the degree of structural changes increased with increasing temperature.

FTIR spectroscopy confirms age-related changes in protein conformation in a new independent dataset of human plasma samples

The loss of proteostasis is a key hallmark of aging and has been well documented using several model systems. However, in biofluids such as blood plasma, little is known about how the loss of proteostasis affects protein conformation during aging. Our previous work has demonstrated age-related changes in protein conformation in human plasma samples using FTIR spectroscopy and conformation-specific antibodies. To prove the potential of spectroscopy to detect slight changes in protein secondary structure during aging, we have applied the same methodology to a new and independent set of 24 human plasma samples from donors with ages ranging from 40 to 75 years. The results clearly show that from middle to old age there is a decrease in antiparallel β-sheet structures and an increase in intermolecular β-sheets, indicative of an increase in aggregation-prone proteins in human plasma over time. This confirms the potential of FTIR spectroscopy as a technique to evaluate protein conformational changes related to health and disease and as a suitable method to be used in a clinical setting to produce quick and reliable results.

Combined effects of high-pressure processing and pre-emulsified sesame oil incorporation on physical, chemical, and functional properties of reduced-fat pork batters

In this study, the changes in emulsion stability, colour, textural properties, and protein secondary structure of reduced-fat pork batters (50% pork back-fat and 50% pre-emulsified sesame oil) treated under different pressures (0.1, 200 and 400 MPa) were investigated. The emulsion stability, cooking yield, L* value, texture properties, initial relaxation times of T2b, T21, and T22, and peak ratios of P21 in the samples treated under 200 and 400 MPa significantly increased (p < 0.05) compared with those at 0.1 MPa, but the a* and b* values, and the peak ratio of P22 significantly decreased (p < 0.05). The sample treated at 200 MPa exhibited the best emulsion stability, textural properties, water-holding capacity and sensory scores among the samples. High-pressure processing induced structural changes from α-helical to β-sheet, β-turn, and random coil structures, enhancing protein-water incorporation and lowering water mobility. High-pressure processing and pre-emulsified sesame oil improved the techno-functional properties and emulsion stability of reduced-fat pork batters.

Effects of different thawing methods on microstructure and the biochemical properties of tilapia (Oreochromis niloticus) fillets during frozen storage

AbstractThis study investigated the effects of different thawing methods (water immersion thawing [WIT, 25 °C], air thawing [AT, 25 °C] and refrigerator thawing [RT, 25 °C]) on the biochemical properties and microstructure of tilapia (Oreochromis niloticus) fillets during storage at −18 °C for 6 months. The results indicated that the thawing time for WIT, AT and RT were approximately 7, 83 and 616 min, respectively. Thawing and cooking losses in the RT samples were significantly lower than those in WIT and AT samples (P &lt; 0.05). The microstructural integrity of RT samples was less compromised than that of WIT and AT treated samples. Ca2+‐ATPase activity and SH content decreased with increasing storage time and the frozen storage time. Compared with the other two thawing groups during frozen storage, RT had the highest fluorescence, which was significant for the quality of tilapia fillets. However, no significant difference (P &lt; 0.05) was observed in protein secondary structure changes, especially β‐sheets and β‐turns. Therefore, RT is suggested to be an effective thawing method to minimise quality change during frozen storage and the frozen storage time has a greater impact on its quality. These results demonstrate the interaction between frozen storage and thawing processes on selected quality parameters.

FTIR Spectroscopy as a Tool to Study Age-Related Changes in Cardiac and Skeletal Muscle of Female C57BL/6J Mice.

Studying aging is important to further understand the molecular mechanisms underlying this physiological process and, ideally, to identify a panel of aging biomarkers. Animals, in particular mice, are often used in aging studies, since they mimic important features of human aging, age quickly, and are easy to manipulate. The present work describes the use of Fourier Transform Infrared (FTIR) spectroscopy to identify an age-related spectroscopic profile of the cardiac and skeletal muscle tissues of C57BL/6J female mice. We acquired ATR-FTIR spectra of cardiac and skeletal muscle at four different ages: 6; 12; 17 and 24 months (10 samples at each age) and analyzed the data using multivariate statistical tools (PCA and PLS) and peak intensity analyses. The results suggest deep changes in protein secondary structure in 24-month-old mice compared to both tissues in 6-month-old mice. Oligomeric structures decreased with age in both tissues, while intermolecular β-sheet structures increased with aging in cardiac muscle but not in skeletal muscle. Despite FTIR spectroscopy being unable to identify the proteins responsible for these conformational changes, this study gives insights into the potential of FTIR to monitor the aging process and identify an age-specific spectroscopic signature.

Emulsification through oil addition on the properties of yellowfin tuna ( Thunnus albacares ) paste

In this study, the effects of different amounts of oil addition on the properties of tuna paste were investigated. The whiteness gradually improved with the oil addition. The water holding capacity increased from 0.28 without oil addition to a peak of 0.47 with 15% oil addition before decreasing to 0.21% at 35% oil addition. Changes in properties were measured by a rotational rheometer. Changes in protein secondary structure were evaluated by Fourier transform infrared spectroscopy. The particle size measurements showed that the maximum amount of protein available to bind oil in the emulsification system is ~ 20% and excessive oil will destabilize the system. The oil droplet distribution in the emulsified system was shown by the optical microscope. The differential scanning calorimetry revealed that the oil addition could improve the transfer temperature of actin when the addition amount less than 20%. Overall, plant oil is suggested to improve the rough taste of processed tuna products. Novelty impact statement This work investigates the effects of sunflower seed oil addition on the properties of tuna paste. We found that oil addition greatly changed the properties of tuna paste, such as whiteness, WHC, and rheology properties, thus affecting the taste of tuna paste. The present results showed that adding a suitable amount of oil can improve the property of tuna paste through lipid–protein interaction, thus not only potentially overcoming current limitation of tuna processing technology, but also encourages food processors to produce different forms of tuna products to satisfy consumers with different preferences.

Structural Changes in Insulin at a Soft Electrochemical Interface.

Understanding the interaction of proteins at interfaces, which occurs at or within cell membranes and lipoprotein vesicles, is central to our understanding of protein function. Therefore, new experimental approaches to understand how protein structure is influenced by protein-interface interactions are important. Herein we build on our previous work exploring electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) to investigate changes in protein secondary structure that are modulated by protein-interface interactions. The ITIES provides an experimental framework to drive protein adsorption at an interface, allowing subsequent spectroscopic analysis (e.g., Fourier transform infrared spectroscopy) to monitor changes in protein structure. Here, we reveal that the interaction between insulin and the interface destabilizes native insulin secondary structure, promoting formation of α helix secondary structures. These structural alterations result from protein-interface rather than protein-protein interactions at the interface. Although this is an emerging approach, our results provide a foundation highlighting the value of the ITIES as a tool to study protein structure and interactions at interfaces. Such knowledge may be useful to elucidate protein function within biological systems or to aid sensor development.

Changes in the Structure and Digestibility of Myoglobin Treated With Sodium Chloride

ObjectivesChanges in the structure of myoglobin affect its digestibility and myoglobin can’t be completely broken down of pepsin. The exact mechanism of this breakdown is not clear. It can be inferred that myoglobin is broken down into polypeptides whose structures do not fully conform to the spatial characteristics of digestive enzymes. Myoglobin dissolution in different salt concentrations and changes in secondary structure were examined by spectroscopic examination. The molecular dynamics simulation was used to study the stability of these structural changes and their combination with digestive enzymes. Finally, since the products of digestion are determined by the catalytic centers of digestive enzymes, the substrate channel is extended to study the relationship between digestive enzymes and substrates. MethodsIn this study, different concentrations of sodium chloride were added for a certain period of time in advance to detect changes in the secondary structure of myoglobin, leading to changes in digestibility. Myoglobin and digestive enzymes were docked for molecular dynamics simulations to analyze the energy and structural changes in the interactions between substrates and proteins. ResultsSalt-treated protein can affect the secondary structure changes of protein. High concentration of salt-treated protein will lead to protein aggregation and denaturation, affecting digestibility. Low concentration of salt-treated protein may lead to exposure of sleeping areas, reducing digestibility. In terms of structure, salt ions lead to changes in the bonding of amino acids in the protein and affect the substrate’s entry into the enzyme activity center. ConclusionsTreatment of myoglobin with different salt concentrations did not change its tertiary structure but low salt concentrations lowered its digestibility, probably due to salt ions altering a number of key amino acid bonds, making the structure more stable and less susceptible to digest. Some low molecular weight peptides remain after pepsin digestion. This may be due to the distance between the key amino acids in the active catalytic center of pepsin being insufficient to form stable conformations with small peptides. Funding SourcesThis work was supported by the grants from NSFC (32072211).