Disulfide bond within µ-calpain active site inhibits activity and autolysis

Pathological Impact of Redox Post-Translational Modifications

Oxidative stress is involved in the development of several pathologies. The different reactive oxygen species (ROS) produced during oxidative stress are at the origin of redox post-translational modifications (PTMs) on proteins and impact nucleic acids and lipids. This review provides an overview of recent data on cysteine and methionine oxidation and protein carbonylation following oxidative stress in a pathological context. Oxidation, like nitration, is a selective process and not all proteins are impacted. It depends on multiple factors, including amino acid environment, accessibility, and physical and chemical properties, as well as protein structures. Thiols can undergo reversible oxidations and others that are irreversible. On the contrary, carbonylation represents irreversible PTM. To date, hundreds of proteins were shown to be modified by ROS and reactive nitrogen species (RNS). We reviewed recent advances in the impact of redox-induced PTMs on protein functions and activity, as well as its involvement in disease development or treatment. These data show a complex situation of the involvement of redox PTM on the function of targeted proteins. Many proteins can have their activity decreased by the oxidation of cysteine thiols or methionine S-methyl thioethers, while for other proteins, this oxidation will be activating. This complexity of redox PTM regulation suggests that a global antioxidant therapeutic approach, as often proposed, is unlikely to be effective. However, the specificity of the effect obtained by targeting a cysteine or methionine residue to be able to inactivate or activate a particular protein represents a major interest if it is possible to consider this targeting from a therapeutic point of view with our current pharmacological tools. Antioxid. Redox Signal. 41, 152-180.

Synergistic Effects of High-Intensity Ultrasound Combined with L-Lysine for the Treatment of Porcine Myofibrillar Protein Regarding Solubility and Flavour Adsorption Capacity

This study aimed to investigate the synergistic effects of high-intensity ultrasound (0, 5, 10, 15, and 20 min) in combination with L-lysine (15 mM) on improving the solubility and flavour adsorption capacity of myofibrillar proteins (MPs) in low-ion-strength media. The results revealed that the ultrasound treatment for 20 min or the addition of L-lysine (15 mM) significantly improved protein solubility (p < 0.05), with L-lysine (15 mM) showing a more pronounced effect (p < 0.05). The combination of ultrasound treatment and L-lysine further increased solubility, and the MPs treated with ultrasound at 20 min exhibited the best dispersion stability in water, which corresponded to the lowest turbidity, highest absolute zeta potential value, and thermal stability (p < 0.05). Based on the reactive and total sulfhydryl contents, Fourier transform infrared spectroscopy, and fluorescence spectroscopy analysis, the ultrasound treatment combined with L-lysine (15 mM) promoted the unfolding and depolymerization of MPs, resulting in a larger exposure of SH groups on the surface, aromatic amino acids in a polar environment, and a transition of protein conformation from α-helix to β-turn. Moreover, the combined treatment also increased the hydrophobic bonding sites, hydrogen-bonding sites, and electrostatic effects, thereby enhancing the adsorption capacity of MPs to bind kenone compounds. The findings from this study provide a theoretical basis for the production and flavour improvement of low-salt MP beverages and the utilisation of meat protein.

Formation of the calpain-1/calpastatin complex promotes activation of calpain-1 under oxidizing conditions

Calpains are cysteine proteinases responsible for many biological roles in muscle, including protein degradation, muscle growth, and myoblast fusion. Calpains are inhibited by calpastatin, an endogenous inhibitor. Other factors, such as variations in pH, ionic strength, and oxidation influence calpain activity. This study aimed to determine the extent to which oxidation influences calpastatin inhibition of calpain-1. A series of order of addition assays were used to determine calpain-1 calcium activation and autolysis after exposure to an oxidizing agent (n-ethylmaleimide [NEM] or hydrogen peroxide [H2O2]. In the first series, purified calpastatin was added to the assay before or after oxidizing exposure at 165 mM NaCl, pH 6.5. In the second series, incubation buffer ionic strength (165 mM or 295 mM NaCl) was evaluated. The inhibitory activities of purified porcine calpastatin, purified human calpastatin domain I, or a subdomain B inhibitor peptide were evaluated in the third series. In the fourth series, a maleimide-polyethylene glycol molecule (MAL-PEG; MW = 5,000 Dalton) was used to evaluate the accessibility of free sulfhydryl groups and tagging of calpain-1 under each condition through a molecular weight shift assay. Results from this study indicate that autolysis of calpain-1, when used as an indicator of activation, occurred when the calpain-1/calpastatin complex was exposed to an oxidant or cysteine modifier such as NEM. However, when calpain-1 was exposed to the cysteine modifier before calpastatin, autolysis of calpain-1 did not occur or was significantly decreased (P < 0.05). Irreversible modification of cysteine residues by NEM prevented activation of calpain-1 in the absence of calpastatin, but if the cysteine modification is potentially reversible (H2O2), calpain-1 activity can be recovered. Results from this study indicate that when calpastatin is bound to calpain-1, calpain-1 activation can occur even after being exposed to a cysteine modifier (NEM) or hydrogen peroxide (H2O2). Calpain-1 is not tagged with maleimide-polyethylene glycol (MAL-PEG) in the presence of calpastatin, indicating that calpastatin blocks or covers free cysteines on calpain-1 from modification. Moreover, exposure to calpain-1/calpastatin complex with a cysteine modifier allows activation of calpain-1, indicating that the inhibitory action of calpastatin is compromised. These results indicate a regulatory role for calpastatin that is not inhibitory but protective for calpain-1.

Effect of ultimate pH on quality of aged Longissimus dorsi muscle of Zebu Nellore (Bos indicus) during long-term frozen storage

Despite the relatively high occurrence of bovine meat with intermediate to high ultimate pH (pHu), there is a lack of studies focused on the effects of long-term conventional air-blasting freezing storage on quality parameters of commercial beefs of Zebu Nellore (Bos indicus) with varying pHu ranges. The objective of this work was to evaluate the influence of pHu ranges [normal (≤5.79), intermediate (5.80 to 6.19), and high (≥6.20)] and long-term frozen storage on quality parameters of aged Longissimus dorsi beefs of Zebu Nellore (Bos indicus). The aging conditions were set at 2 °C for 14 days, while the freezing conditions were set at - 20 °C, and samples were collected after 3, 6, 9, and 12 months of storage. The results indicated that the pHu influenced meat quality parameters, as well as the chemical forms of myoglobin, which changed throughout the frozen storage, leading to a brighter red color, especially for the normal pHu beef samples, likely due to increased oxymyoglobin content. Frozen storage improved tenderness, with high pHu beef samples being the more tender after 12 months, potentially due to lower protein oxidation, as measured by the carbonyl content. Increased drip loss was observed over freezing time, with a concomitant decrease in protein solubility, especially for myofibrillar and sarcoplasmic proteins, which differed among the pHu ranges. These findings are valuable for determining freezing time as a preservation strategy to maintain beef quality within different pHu ranges.

Lipid Peroxidation Products Influence Calpain-1 Functionality In Vitro by Covalent Binding

The objective of the current study was to evaluate the effects of lipid peroxidation products, malondialdehyde (MDA), hexenal, and 4-hydroxynonenal (HNE), on calpain-1 function, and liquid chromatography and tandem mass spectrometry (LC-MS/MS) identification of adducts on calpain-1. Calpain-1 activity slightly increased after incubation with 100 μM MDA but not with 500 and 1000 μM MDA. However, calpain-1 activity was lowered by hexenal and HNE at 100, 500, and 1000 μM. No difference in calpain-1 autolysis was observed between the control and 1000 μM MDA. However, 1000 μM hexenal and HNE treatments slowed the calpain-1 autolysis. Adducts of MDA were detected on glutamine, arginine, lysine, histidine, and asparagine residues via Schiff base formation, while HNE adducts were detected on histidine, lysine, glutamine, and asparagine residues via Michael addition. These results are the first to demonstrate that lipid peroxidation products can impact calpain-1 activity in a concentration-dependent manner and may impact the development of meat tenderness postmortem.

Considering Two Aspects of Fish Welfare on African Catfish (Clarias gariepinus) Fillet throughout Postmortem Condition: Efficiency and Mechanisms

Knowledge about fish welfare and its impact on fish fillet quality is still insufficient. Therefore, the influence of two aspects of fish welfare (slaughtering method: bled and unbled fish; fish stock densities: 90, 120, and 150 kg·m^-3) on African catfish fillet quality during postmortem conditions was investigated. The aim of study was to determine (i) the efficiency of bleeding on oxidation progress and (ii) the influence of stock density on fillet quality. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a higher protein loss in the unbled than in the bled groups, especially in the heavy myosin chain (MHC) band. However, density did not show any influence on protein profile. Western blot analysis showed fewer oxidized carbonyls in the bled than in the unbled groups; higher oxidation development, microbial growth, and lower hardness were observed in unbled fillets. Additionally, hardness was higher at 90 and 120 kg·m^-3 densities in bled fillet compared to 150 kg·m^-3. The first three days of storage showed a higher oxidation rate in unbled fillets than in bled fillets, confirming the contribution of hemoglobin to oxidation development with different mechanisms of protein oxidation. The obtained results revealed the same fillet quality in all aspects at either 90 or 120 (kg·m^-3) stock densities, which would suggest 120 kg·m^-3 for the fishery industry. However, higher stocking density in this study would not be appropriate for fish welfare.

Biological function, mediate cell death pathway and their potential regulated mechanisms for post-mortem muscle tenderization of PARP1: A review

Tenderness is a key attribute of meat quality that affects consumers' willingness to purchase meat. Changes in the physiological environment of skeletal muscles following slaughter can disrupt the balance of redox homeostasis and may lead to cell death. Excessive accumulation of reactive oxygen species (ROS) in the myocytes causes DNA damage and activates poly ADP-ribose polymerase 1 (PARP1), which is involved in different intracellular metabolic pathways and is known to affect muscle tenderness during post-slaughter maturation. There is an urgent requirement to summarize the related research findings. Thus, this paper reviews the current research on the protein structure of PARP1 and its metabolism and activation, outlines the mechanisms underlying the function of PARP1 in regulating muscle tenderness through cysteine protease 3 (Caspase-3), oxidative stress, heat shock proteins (HSPs), and energy metabolism. In addition, we describe the mechanisms of PARP1 in apoptosis and necrosis pathways to provide a theoretical reference for enhancing the mature technology of post-mortem muscle tenderization.

Post-Harvest Strategies to Improve Tenderness of Underutilized Mature Beef: A Review

Beef muscles from mature cows and bulls, especially those originating from the extremities of the carcass, are considered as underutilized due to unsatisfactory palatability. However, beef from culled animals comprises a substantial proportion of the total slaughter in the US and globally. Modern consumers typically favor cuts suitable for fast, dry-heat cookery, thereby creating challenges for the industry to market inherently tough muscles. In general, cull cow beef would be categorized as having a lower extent of postmortem proteolysis compared to youthful carcasses, coupled with a high amount of background toughness. The extent of cross-linking and resulting insolubility of intramuscular connective tissues typically serves as the limiting factor for tenderness development of mature beef. Thus, numerous post-harvest strategies have been developed to improve the quality and palatability attributes, often aimed at overcoming deficiencies in tenderness through enhancing the degradation of myofibrillar and stromal proteins or physically disrupting the tissue structure. The aim of this review is to highlight existing and recent innovations in the field that have been demonstrated as effective to enhance the tenderness and palatability traits of mature beef during the chilling and postmortem aging processes, as well as the use of physical interventions and enhancement.

The Changes Occurring in Proteins during Processing and Storage of Fermented Meat Products and Their Regulation by Lactic Acid Bacteria

Protein, which is the main component of meat, is degraded and oxidized during meat fermentation. During fermentation, macromolecular proteins are degraded into small peptides and free amino acids, and oxidation leads to amino acid side chain modification, molecular crosslinking polymerization, and peptide chain cleavage. At different metabolic levels, these reactions may affect the protein structure and the color, tenderness, flavor, and edible value of fermented meat products. Lactic acid bacteria are currently a research hotspot for application in the fermented meat industry. Its growth metabolism and derivative metabolites formed during the fermentation of meat products regulate protein degradation and oxidation to a certain extent and improve product quality. Therefore, this paper mainly reviews the changes occurring in proteins in fermented meat products and their effects on the quality of the products. Referring to studies on the effects of lactic acid bacteria on protein degradation and oxidation from all over the world, this review aims to provide a relevant reference for improving the quality of fermented meat products.

Muscle protein oxidation and functionality: a global view of a once neglected phenomenon

Muscle is a highly organized apparatus with a hierarchicmicrostructure that offers the protection of cellular components againstreactive oxygen species (ROS). However, fresh meat immediately postmortem andmeat undergoing processing become susceptible to oxidation due to physicaldisruption and the influx of molecular oxygen. Upon the activation byendogenous prooxidants, oxygen species are rapidly produced, and bothmyofibrillar and sarcoplasmic proteins become their primary targets. Direct ROSattack of amino acid sidechains and peptide backbone leads to proteinconformational changes, conversion to carbonyl and thiol derivatives, andsubsequent aggregation and polymerization. Interestingly, mild radical andnonradical oxidation enables orderly protein physicochemical changes, which explainswhy gels formed by ROS-modified myofibrillar protein has improved rheologicalproperties and binding potential in comminuted meat and meat emulsions. Theincorporation of phenolic and other multi-functional compounds promotes gelnetwork formation, fat emulsification, and water immobilization; however,extensive protein modification induced by high levels of ROS impairs proteinfunctionality. Now recognized to be a natural occurrence, once-neglectedprotein oxidation has drawn much interest and is being intensively studiedwithin the international community of meat science. This review describes thehistory and evolution of muscle protein oxidation, the mechanism andfunctionality impact hereof, and innovative oxidant/antioxidant strategies tocontrol and manipulate oxidation in the context of meat processing, storage,and quality. It is hoped that the review will stimulate in-depth discussion of scientificas well as industrial relevance and importance of protein oxidation and inspirerobust international collaboration in addressing this global challenge.&nbsp;

Freezing of meat and aquatic food: Underlying mechanisms and implications on protein oxidation

Over the recent decades,protein oxidation in muscle foods has gained increasing research interests as it is known that protein oxidation can affect eating quality and nutritional value of meat and aquatic products. Protein oxidation occurs during freezing/thawing and frozen storage of muscle foods, leading to irreversible physicochemical changes and impaired quality traits. Controlling oxidative damage to muscle foods during such technological processes requires a deeper understanding of the mechanisms of freezing-induced protein oxidation. This review focus on key physicochemical factors in freezing/thawing and frozen storage of muscle foods, such as formation of ice crystals, freeze concentrating and macromolecular crowding effect, instability of proteins at the ice-water interface, freezer burn, lipid oxidation, and so on. Possible relationships between these physicochemical factors and protein oxidation are thoroughly discussed. In addition, the occurrence of protein oxidation, the impact on eating quality and nutrition, and controlling methods are also briefly reviewed. This review will shed light on the complicated mechanism of protein oxidation in frozen muscle foods.

Meat tenderness: advances in biology, biochemistry, molecular mechanisms and new technologies

Meat tenderness is an important quality trait critical to consumer acceptance, and determines satisfaction, repeat purchase and willingness-to-pay premium prices. Recent advances in tenderness research from a variety of perspectives are presented. Our understanding of molecular factors influencing tenderization are discussed in relation to glycolysis, calcium release, protease activation, apoptosis and heat shock proteins, the use of proteomic analysis for monitoring changes, proteomic biomarkers and oxidative/nitrosative stress. Each of these structural, metabolic and molecular determinants of meat tenderness are then discussed in greater detail in relation to animal variation, postmortem influences, and changes during cooking, with a focus on recent advances. Innovations in postmortem technologies and enzymes for meat tenderization are discussed including their potential commercial application. Continued success of the meat industry relies on ongoing advances in our understanding, and in industry innovation. The recent advances in fundamental and applied research on meat tenderness in relation to the various sectors of the supply chain will enable such innovation.

Partial Purification of Peroxiredoxin-2 From Porcine Skeletal Muscle

Fresh meat quality is adversely affected by protein oxidation. However, a fundamental understanding of the diverse factors that influence protein oxidation in postmortem muscle remains elusive. Peroxiredoxin-2 (Prdx2), an antioxidant protein, is more abundant in tough meat based on instrumental tenderness; however, the role of Prdx2 in postmortem skeletal muscle is unknown. Therefore, the objective was to develop a method to purify Prdx2 from the diaphragm, psoas major, and longissimus lumborum. Proteins soluble at low ionic strength were extracted, dialyzed, clarified, and loaded onto a Q-Sepharose anion exchange column equilibrated with TEM (pH 7.4). In all preparations, Prdx2 eluted between about 75 and 115 mM NaCl. Immunoreactive fractions were dialyzed against TEM (pH 8.0), clarified, and loaded onto a DEAE-650S anion exchange column. In all preparations, Prdx2 eluted between approximately 55 and 75 mM NaCl. Immunoreactive fractions were concentrated and loaded onto a Superose-12 size exclusion column. Prdx2 was detected between 14 and 16 mL, and these fractions were concentrated and reduced with 0.5% 2-mercaptoethanol. A final pass over the Superose-12 column was conducted, and Prdx2 was detected in 2 peaks from 11–12 mL and 15–16 mL. Fractions 15–16 were pooled and retained for further experiments. The elution profile of Prdx2 in all 3 muscles was similar. The iden- tification of the primary protein was confirmed with liquid chromatography with tandem mass spectrometry. The purity of Prdx2 off the final Superose-12 column was approximately 33%, 52%, and 47% pure in the diaphragm, psoas major, and longissimus lumborum, respectively. This is the first report of a method to partially purify Prdx2 from skeletal muscle.

μ-Calpain oxidation and proteolytic changes on myofibrillar proteins from Coregonus Peled in vitro

The purpose of this study was to investigate the structural properties of μ-calpain induced by hydroxyl radical oxidation and its effect on the degradation of myofibrillar protein (MP) from the dorsal muscles of Coregonus peled. The carbonyl and sulfhydryl content of μ-calpain changed significantly after oxidation. The content of α-helix in the secondary structure decreased from 0.825 to 0.232 and the changes in intrinsic fluorescence and ultraviolet (UV) absorption spectra indicated that oxidation could cause the expansion and aggregation of µ-calpain molecules. Changes in µ-calpain structure could improve the activity of µ-calpain, reaching the highest value at 0.5 mM H₂O₂. The highest µ-calpain activity facilitate the degradation of unoxidized MP, while the degradation of oxidized MP was facilitated at the 1 mM H₂O₂. Thus, our results provide a scientific basis for the interaction mechanism among hydroxyl radical oxidation, µ-calpain, and MP degradation.

Redox-Mediated Post-Translational Modifications of Proteolytic Enzymes and Their Role in Protease Functioning

Proteolytic enzymes play a crucial role in metabolic processes, providing the cell with amino acids through the hydrolysis of multiple endogenous and exogenous proteins. In addition to this function, proteases are involved in numerous protein cascades to maintain cellular and extracellular homeostasis. The redox regulation of proteolysis provides a flexible dose-dependent mechanism for proteolytic activity control. The excessive reactive oxygen species (ROS) and reactive nitrogen species (RNS) in living organisms indicate pathological conditions, so redox-sensitive proteases can swiftly induce pro-survival responses or regulated cell death (RCD). At the same time, severe protein oxidation can lead to the dysregulation of proteolysis, which induces either protein aggregation or superfluous protein hydrolysis. Therefore, oxidative stress contributes to the onset of age-related dysfunction. In the present review, we consider the post-translational modifications (PTMs) of proteolytic enzymes and their impact on homeostasis.

Proteolytic changes of myofibrillar and small heat shock proteins in different bovine muscles during aging: Their relevance to tenderness and water-holding capacity

The objective of this study was to determine the proteolytic changes of myofibrillar and small heat shock proteins (HSPs) in different muscles during aging and to evaluate their relevance to meat quality attributes. From 8 beef carcasses, longissimus lumborum (LL), semimembranosus (SM), and psoas major (PM) muscles were obtained, cut into sections and assigned to various aging periods up to 23d. PM exhibited limited aging potential in quality developments shown by lower extents of shear force, water-holding capacity (WHC), and proteolytic changes, including calpain 1 autolysis, troponin T, and HSP27 compared to LL and SM. Conversely, LL had an increase in tenderization and WHC, which was accompanied with more extended calpain 1 autolysis, proteolysis and HSP27 degradation, compared with other muscles. The results of this study suggest that postmortem proteolytic changes of myofibrillar proteins, small HSPs and apoptotic factors occur in a muscle-specific manner, which is likely attributed to different rate and extent of meat quality developments of each muscle during aging.

Effects of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation in vitro

The aim of this study was to evaluate the effect of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation. In the present study, a hydroxyl radical oxidation system was selected to investigate oxidative modification on µ-calpain activity and its degradation on C. peled myofibrillar protein. When subjected to oxidation, the carbonyl content of µ-calpain significantly increased with the increasing of oxidation levels, and oxidation modification promoted the µ-calpain activity. Incubation of C. peled myofibrillar protein with oxidized µ-calpain resulted in the enhanced degradation of myosin heavy chains, actin, and troponin T, but the degradation of desmin at higher levels of oxidation was slightly inhibited, based on sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting. This study suggests that oxidation treatment of µ-calpain could accelerate myofibrillar proteolysis through regulating the enzyme activity during postmortem aging. PRACTICAL APPLICATION: Endogenous proteases, especially µ-calpain, are reported to be involved in fish softening during early postmortem storage, which is critical to muscle quality. The cysteine residues of proteins are particularly sensitive to oxidation. The investigation of the effect of oxidation on µ-calpain (a cysteine protease) activity allows for the monitoring of its role in the postmortem proteolysis of fish myofibrils and the associated softening of fish meat, in an attempt to minimize this softening.

Effect of Different Packaging Methods on Protein Oxidation and Degradation of Grouper (Epinephelus coioides) During Refrigerated Storage

This study investigates the effect of different packaging methods-namely, air packaging (AP), vacuum packaging (VP), and modified atmosphere packaging (MAP)-on the protein oxidation and degradation of grouper (Epinephelus coioides) fillets during refrigerated storage. The carbonyl group, myofibril fragmentation index, free amino acids, FTIR of myofibrillar proteins, and total protein SDS-PAGE were determined. The results showed that the protein oxidation degree of the fillets gradually increased as the storage time increased. The FTIR results indicated that the secondary structure transformed from an α-helix to an irregular curl. SDS-PAGE confirmed the degradation of the myosin heavy chain, and that myosin gradually occurred during refrigerated storage. Meanwhile, protein oxidation and degradation were highly correlated. Protein degradation was accelerated by protein oxidation in myofibrils, which included the increase of protein surface hydrophobicity and changes of the secondary structure. In fact, the protein oxidation and degradation of the grouper fillets were effectively inhibited by MAP and VP during refrigerated storage, and MAP (30% N2 and 70% CO2) had the best results.

Stress Effects on Meat Quality: A Mechanistic Perspective

Stress inevitably occurs from the farm to abattoir in modern livestock husbandry. The effects of stress on the behavioral and physiological status and ultimate meat quality have been well documented. However, reports on the mechanism of stress effects on physiological and biochemical changes and their consequent effects on meat quality attributes have been somewhat disjointed and limited. Furthermore, the causes of variability in meat quality traits among different animal species, muscle fibers within an animal, and even positions within a piece of meat in response to stress are still not entirely clear. This review 1st summarizes the primary stress factors, including heat stress, preslaughter handling stress, oxidative stress, and other stress factors affecting animal welfare; carcass quality; and eating quality. This review further delineates potential stress-induced pathways or mediators, including AMP-activated protein kinase-mediated energy metabolism, crosstalk among calcium signaling pathways and reactive oxygen species, protein modification, apoptosis, calpain and cathepsin proteolytic systems, and heat shock proteins that exert effects that cause biochemical changes during the early postmortem period and affect the subsequent meat quality. To obtain meat of high quality, further studies are needed to unravel the intricate mechanisms involving the aforementioned signaling pathways or mediators and their crosstalk.

Influence of modified atmosphere packaging on protein oxidation, calpain activation and desmin degradation of beef muscles

BACKGROUND

Protein oxidation is widespread in biochemical systems. The objective of the study was to investigate the differences in protein oxidation, μ-calpain activity, desmin proteolysis and protein solubility of beef psoas major (PM) and semi-membranosus (SM) muscles under three packaging systems during postmortem ageing. At 24 h postmortem, beef muscles were packaged respectively in air-permeable film overwrap (AP), vacuum pack (VP) or modified atmosphere (MAP, 80% O₂ + 20% CO₂ ), and then displayed for 10 days at 4 °C.

RESULTS

Carbonyl group values and thiol group content were significantly influenced by packaging type and storage time. The SM muscles from AP and MAP showed greater μ-calpain activity compared to VP. Desmin of PM and SM from AP and MAP samples showed decreased proteolysis compared with VP.

CONCLUSION

The results suggested that the inhibition of μ-calpain activity of beef samples from AP and MAP could be closely associated with protein oxidation which further lowered the level of desmin degradation compared to VP. © 2017 Society of Chemical Industry.

Effect and mechanism of calpains on pediatric lobar pneumonia

Lobar pneumonia, one of the community-acquired pneumonia (CAP), is a common pediatric low respiratory tract infection. Calpains are Ca²⁺-activated cysteine proteases whose activation mechanism is elusive. The present study was undertaken to detect the role and mechanism of calpains in pediatric lobar pneumonia. The human acute lung infection model (ALIM) was constructed and infected by Streptococcus. Enzyme-linked immunosorbent assay (ELISA) was used to measure interleukin (IL)-6, IL-8 and tumor necrosis factor (TNF)-α. We observed the lactate dehydrogenase (LDH) release, calpains activity and calpain inhibitor effects in ALIM. The expression of proliferating cell nuclear antigen (PCNA) protein was quantified by western blotting. Then the effects of calpain 1 and 2 knockdown on expressions of inflammation factors and PCNA protein, LDH release and apoptosis were evaluated in lung MRC-5 cells. In constructed ALIM, expressions of IL-6 (P < 0.01), IL-8 (P < 0.01), TNF-α (P < 0.05) and PCNA protein (P < 0.05) were significantly reduced by the calpain inhibitor. Expressions of IL-6, IL-8, TNF-α, PCNA protein and relative LDH release were statistically reduced by the small interfering (si) RNA-calpain 1 and 2 in MRC-5 cells (P < 0.05). Calpains silence increased apoptotic cells from 5% (negative control) to more than 20% in MRC-5 cells. The present study suggests that calpains possess a significant effect on inflammations, cell proliferation and apoptosis. Suppression of calpains may provide a potential therapeutic target of lobar pneumonia.

Effect of protein S-nitrosylation on autolysis and catalytic ability of μ-calpain

The effect of S-nitrosylation on the autolysis and catalytic ability of μ-calpain in vitro in the presence of 50μM Ca(2 +) was investigated. μ-Calpain was incubated with different concentrations of nitric oxide donor S-nitrosoglutathione (GSNO) and subsequently reacted with purified myofibrils. Results showed that the amount of 80kDa μ-calpain subunit significantly decreased as GSNO increased from 0 to 300μM, but increases of GSNO to 300, 500 and 1000μM did not result in further inhibition. The catalytic ability of nitrosylated μ-calpain to degrade titin, nebulin, troponin-T and desmin was significantly reduced when the GSNO concentration was higher than 300μM. The cysteine residues of μ-calpain at positions 49, 351, 384, and 592 in the catalytic subunit and at 142 in small subunit were S-nitrosylated, which could be responsible for decreased μ-calpain activity. Thus, S-nitrosylation can negatively regulate the activation of μ-calpain resulting in decreased proteolytic ability on myofibrils.

Protein oxidation affects proteolysis in a meat model system

The effect of hydrogen peroxide-induced protein oxidation and pH (4.8 and 5.2) on meat proteolysis was investigated in a meat model system for dry fermented sausages. In oxidised samples, increased protein carbonyl contents and decreased thiol concentrations were found. The initial concentration of protein carbonyls was significantly lower in oxidised samples at pH4.8 than in ones at pH5.2, but after ten days comparable levels were reached. The inhibition of proteolysis by the addition of a protease inhibitor cocktail did not influence protein oxidation. Yet, proteolysis was negatively affected by low pH values as well as by oxidation, resulting in a reduced release of amino acids during ripening.

Effect of nitric oxide on μ-calpain activation, protein proteolysis, and protein oxidation of pork during post-mortem aging

The aim of the current research was to examine the influence of nitric oxide (NO) on calpain activation, protein proteolysis, and oxidation in post-mortem pork. Five longissimus muscles were removed from carcass after slaughter, and samples were incubated with water, nitric oxide synthase (NOS) inhibitor, or NO donor for 24 h at 4 °C. The samples were taken out and then stored under 4 °C for 1, 4, and 7 d. Results showed that autolysis of μ-calpain increased by incubation with NOS inhibitor after storage for 1 d (P<0.05). Degradation of titin and nebulin increased by treatment of NOS inhibitor among three treatments (P<0.05). Higher levels of protein oxidation were observed after samples incubated with NO donor than treatment of NOS inhibitor (P<0.05). These data indicated that NO could participate in regulating calpain activation and its proteolysis activity during post-mortem aging.

Influence of supplemental vitamin C on postmortem protein degradation and fatty acid profiles of the longissimus thoracis of steers fed varying concentrations of dietary sulfur

The objective was to examine the effects of supplemental vitamin C (VC) on postmortem protein degradation and fatty acid profiles of cattle receiving varying concentrations of dietary sulfur (S). A longissimus muscle was collected from 120 Angus-cross steers assigned to a 3 × 2 factorial, evaluating three concentrations of dietary S (0.22, 0.34, and 0.55%) and two concentrations of supplemental VC (0 or 10 g h(-1)d(-1)). Increasing dietary S and VC supplementation (P<0.001) increased the percent polyunsaturated fatty acids of steaks. Addition of VC tended to increase (P = 0.09) both Fe and 2-thiobarbituric acid content of longissimus thoracis. Increasing S increased (P = 0.03) the proportion of 80-kDa subunit of μ-calpain. Addition of VC within the high S treatment increased (P = 0.05) the abundance of 76-kDa subunit of μ-calpain. Increasing S decreased troponin T degradation (P = 0.07) and protein carbonylation (P<0.01). Supplemental VC appears to alleviate negative effects of high S on autolysis of μ-calpain and protein degradation.

Evidence of decreased muscle protein turnover in gilts selected for low residual feed intake

The objective of this study was to evaluate the contribution of muscle protein turnover (synthesis and degradation) to the biological basis for genetic differences in finisher pigs selected for residual feed intake (RFI). Residual feed intake is defined as the difference between expected feed intake (based on the achieved rate of BW gain and backfat depth of individual pigs) and the observed feed intake of the individual pig. We hypothesized that protein turnover would be reduced in pigs selected for low RFI. Twelve gilts from a line selected for 7 generations for low RFI and 12 from a contemporary line selected for 2 generations for high RFI were paired by age and BW and fed a standard corn-soybean diet for 6 wk. Pigs were euthanized, muscle and liver samples were collected, and insulin signaling, protein synthesis, and protein degradation proteins were analyzed for expression and activities. Muscle from low RFI pigs tended to have less μ- and m-calpain activities (P = 0.10 and 0.09, respectively) and had significantly greater calpastatin activity and a decreased μ-calpain:calpastatin activity ratio (P < 0.05). Muscle from low RFI pigs had less 20S proteasome activity compared with their high RFI counterparts (P < 0.05). No differences in insulin signaling intermediates and translation initiation signaling proteins [mammalian target of rapamycin (mTOR) pathway] were observed (P > 0.05). Postmortem proteolysis was determined in the LM from the eighth generation of the low RFI pigs versus their high RFI counterparts (n = 9 per line). Autolysis of μ-calpain was decreased in the low RFI pigs and less troponin-T degradation product was observed at 3 d postmortem (P < 0.05), indicating slowed postmortem proteolysis during aging in the low RFI pigs. These data provide significant evidence that less protein degradation occurs in pigs selected for reduced RFI, and this may account for a significant portion of the increased efficiency observed in these animals.

Modulation by Syk of Bcl-2, calcium and the calpain-calpastatin proteolytic system in human breast cancer cells

Syk is a 72kDa non-receptor tyrosine kinase that is best characterized in hematopoietic cells. While Syk is pro-tumorigenic in some cancer cell types, it also has been reported as a negative regulator of metastatic cell growth in others. An examination of the RelA (p65) subunit of NF-κB expressed in MCF7 breast cancer cells indicated that either treatment with pervanadate or stable expression of Syk protected RelA from calpain-mediated proteolysis. Similar results were observed with the tyrosine phosphatase, PTP1B, another sensitive calpain substrate. The activity of calpain in MCF7 cell lysates was inhibited by both treatment with hydrogen peroxide and expression of Syk, the former due to oxidative inactivation of calpain and the latter to enhanced expression of calpastatin (CAST), the endogenous calpain inhibitor. The level of CAST was elevated in the cytosolic fraction of Syk-positive breast cancer cells resulting in more CAST present in complex with calpain in cell lysates. The high levels of CAST coincided with elevated basal levels of calcium-and of intracellular calpain activity-in Syk-expressing cells resulting from decreased levels of Bcl-2, an inhibitor of IP3-receptor-mediated calcium release. The inhibition of cellular calpain stimulated the Syk-mediated enhancement of NF-κB induced by TNF-α, enhanced tyrosine phosphorylation resulting from integrin crosslinking, and increased the localization of Syk to the plasma membrane.