Potential DPP IV Inhibitory Peptides from Dry-Cured Pork Loins after Hydrolysis: An In Vitro and In Silico Study

Peptidyl peptidase IV (DPP-IV) is a pharmacotherapeutic target in type 2 diabetes, and inhibitors of this enzyme are an important class of drugs for the treatment of type 2 diabetes. In the present study, peptides (<7 kDa) isolated from dry-cured pork loins after pepsin and pancreatin hydrolysis were identified by mass spectrometry and tested as potential inhibitors of DPP-IV by the in silico method. Two peptides, namely WTIAVPGPPHS from myomesin (water-soluble fraction, A = 0.9091) and FKRPPL from troponin (salt-soluble fraction, A = 0.8333), were selected as the most promising inhibitors of DPP-IV. Both peptides were subjected to ADMET analysis. Fragments of these peptides showed promising drug-likeness properties as well as favorable absorption, distribution, metabolism, excretion, and toxicity functions, suggesting that they are novel leads in the development of DPP-IV inhibitors from food.

Synergistic recovery and enhancement of gelling properties of oxidatively damaged myofibrillar protein by l-lysine and transglutaminase

The influence of combined Lysine (Lys) and transglutaminase (TG) on the conformation and gelling properties of oxidatively damaged myofibrillar protein (MP) was investigated. The addition of Lys (5 mM) significantly increased the α-helix content (by 47.8%) and decreased the particle size of oxidatively damaged MP, and improved the cooking yield (by 16.8%) and the breaking strength of MP gels (by 65.5%). The treatment with TG (E:S = 1:500) led to a slightly reduced α-helix content but improved breaking strength (by 41.8%) and cooking loss (by 13.3%) of the gels. Their combination (Lys + TG) showed the greatest and synergistic overall improvement, with the set gel displaying a fine, smooth and compact network structure. Notably, the gelling ability of oxidatively damaged MP upon Lys + TG treatment was significantly stronger than that of non-oxidized MP far exceeding its recovery. Therefore, significantly enhanced gelling properties of oxidatively damaged MP can be attained through the combination Lys and TG.

Role of Endogenous Cathepsin L in Muscle Protein Degradation in Olive Flounder (Paralichthys olivaceus) Surimi Gel

We investigated the effect of endogenous cathepsin L on surimi gel produced from olive flounder (Paralichthys olivaceus). The amino acid sequences of six proteins predicted or identified as cathepsin L were obtained from the olive flounder genome database, and a phylogenetic analysis was conducted. Next, cathepsin L activity toward N-α-benzyloxycarbonyl-l-phenylalanyl-l-arginine-(7-amino-4-methylcoumarin) (Z-F-R-AMC) was detected in crude olive flounder extract and a crude enzyme preparation. A considerable decrease in the level of myosin heavy chain (MHC) in surimi occurred during autolysis at 60 °C. In contrast, the levels of actin, troponin-T, and tropomyosin decreased only slightly. To prevent protein degradation by cathepsin L, a protease inhibitor was added to surimi. In the presence of 1.0% protease inhibitor, the autolysis of olive flounder surimi at 60 °C was inhibited by 12.2%; the degree of inhibition increased to 44.2% as the inhibitor concentration increased to 3.0%. In addition, the deformation and hardness of modori gel increased as the inhibitor concentration increased to 2.0%. Therefore, cathepsin L plays an important role in protein degradation in surimi, and the quality of surimi gel could be enhanced by inhibiting its activity.

Purification and Regulation of Pyruvate Kinase from the Foot Muscle of the Anoxia and Freeze Tolerant Marine Snail, Littorina littorea

The intertidal marine snail, Littorina littorea, has evolved to survive bouts of anoxia and extracellular freezing brought about by changing tides and subsequent exposure to harsh environmental conditions. Survival in these anoxic conditions depends on the animals entering a state of metabolic rate depression in order to maintain an appropriate energy production-consumption balance during periods of limited oxygen availability. This study investigated the kinetic, physical, and regulatory properties of pyruvate kinase (PK), which catalyzes the final reaction of aerobic glycolysis, from foot muscle of L. littorea to determine if the enzyme is differentially regulated in response to anoxia and freezing exposure. PK purified from foot muscle of anoxic animals exhibited a lower affinity for its substrate phosphoenolpyruvate than PK from control and frozen animals. PK from anoxic animals was also more sensitive to a number of allosteric regulators, including alanine and aspartate, which are key anaerobic metabolites in L. littorea. Furthermore, PK purified from anoxic and frozen animals exhibited greater stability compared to the non-stressed control animals, determined through high-temperature incubation studies. Phosphorylation of threonine and tyrosine residues was also assessed and demonstrated that levels of threonine phosphorylation of PK from anoxic animals were significantly higher than those of PK from control and frozen animals, suggesting a potential mechanism for regulating PK activity. Taken together, these results suggest that PK plays a role in suppressing metabolic rate in these animals during environmental anoxia exposure.

Optimization of Extraction of Bioactive Peptides from Monkfish (Lophius litulon) and Characterization of Their Role in H2O2-Induced Lesion

Background: Marine fish meat has been widely used for the extraction of bioactive peptides. This study was aimed to optimize the preparation of monkfish muscle peptides (LPs) using response surface methodology (RSM) and explore the antioxidant activities of <1 kDa LPs. Methods: Peptides were prepared from the muscles of monkfish (Lophius litulon), and five proteases were tested to hydrolyze muscle proteins. The hydrolysate that was treated using neutrase showed the highest degree of hydrolysis (DH) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities. Results: The optimized conditions were as follows: water/material ratio of 5.4:1, a time span of 5 h, pH of 7.0, enzyme concentration of 2000 U/g, and temperature of 45 °C; the maximum DPPH scavenging activity and DH were 92.861% and 19.302%, respectively. LPs exhibited appreciable antioxidant activities, including DPPH radical, hydroxyl radical, 2,2′-azinobis-3-ethylbenzthiazoline-6-sulphonate (ABTS) radical, and superoxide anion scavenging activities. LPs attenuated H₂O₂-related oxidative injury in RAW264.7 cells, reduced the reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and increased the superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) levels. Conclusion: We concluded that LPs could be an ideal source of bioactive peptides from monkfish and also have pharmaceutical potential.

Kinetic parameters of human aspartate/asparagine-β-hydroxylase suggest that it has a possible function in oxygen sensing

Human aspartate/asparagine-β-hydroxylase (AspH) is a 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the post-translational hydroxylation of Asp and Asn residues in epidermal growth factor-like domains (EGFDs). Despite its biomedical significance, studies on AspH have long been limited by a lack of assays for its isolated form. Recent structural work has revealed that AspH accepts substrates with a noncanonical EGFD disulfide connectivity (i.e. the Cys 1-2, 3-4, 5-6 disulfide pattern). We developed stable cyclic thioether analogues of the noncanonical EGFD AspH substrates to avoid disulfide shuffling. We monitored their hydroxylation by solid-phase extraction coupled to MS. The extent of recombinant AspH-catalyzed cyclic peptide hydroxylation appears to reflect levels of EGFD hydroxylation observed in vivo, which vary considerably. We applied the assay to determine the kinetic parameters of human AspH with respect to 2OG, Fe(II), l-ascorbic acid, and substrate and found that these parameters are in the typical ranges for 2OG oxygenases. Of note, a relatively high Km for O2 suggested that O2 availability may regulate AspH activity in a biologically relevant manner. We anticipate that the assay will enable the development of selective small-molecule inhibitors for AspH and other human 2OG oxygenases.

Effects of high-speed shear homogenization on the emulsifying and structural properties of myofibrillar protein under low-fat conditions

BACKGROUND

Emulsification is important for food quality and processing functionality. Most emulsification occurs under high-fat conditions that eventually cause health concerns. Protein emulsifiers also have drawbacks such as lower dispersity. This study considered the effects of different high-speed shear homogenization (HSH) speeds on the emulsifying and structural properties of myofibrillar proteins (MPs) under low-fat conditions.

RESULTS

High-speed shear homogenization significantly increased the emulsifying activity and emulsifying stability of MPs at lower speeds (8000 to 14 500 rpm). The primary structure of MP was not altered significantly by HSH, whereas its secondary, tertiary, and quaternary structures were changed. Particle size decreased first and then increased significantly, and reached a minimum when the HSH speed was 14 500 rpm. The absolute zeta potential values increased significantly and the dendritic fibrous structure of sample was destroyed when the speed exceeded 14 500 rpm. High-speed shear homogenization (14 500 rpm) decreased the particle size and unfolded the protein, which improved the emulsifying properties of MPs. Excessive HSH speeds (20 500 rpm or higher) caused an aggregation of MP molecules, which was not conducive to improving their emulsifying properties.

CONCLUSION

Optimal HSH speed was achieved at 14 500 rpm to modify MPs' emulsifying and structural properties under low-fatconditions. © 2019 Society of Chemical Industry.

Effects of high-speed shear homogenization on the emulsifying and structural properties of myofibrillar protein under low-fat conditions

BACKGROUND

Emulsification is important for food quality and processing functionality. Most emulsification occurs under high-fat conditions that eventually cause health concerns. Protein emulsifiers also have drawbacks such as lower dispersity. This study considered the effects of different high-speed shear homogenization (HSH) speeds on the emulsifying and structural properties of myofibrillar proteins (MPs) under low-fat conditions.

RESULTS

High-speed shear homogenization significantly increased the emulsifying activity and emulsifying stability of MPs at lower speeds (8000 to 14 500 rpm). The primary structure of MP was not altered significantly by HSH, whereas its secondary, tertiary, and quaternary structures were changed. Particle size decreased first and then increased significantly, and reached a minimum when the HSH speed was 14 500 rpm. The absolute zeta potential values increased significantly and the dendritic fibrous structure of sample was destroyed when the speed exceeded 14 500 rpm. High-speed shear homogenization (14 500 rpm) decreased the particle size and unfolded the protein, which improved the emulsifying properties of MPs. Excessive HSH speeds (20 500 rpm or higher) caused an aggregation of MP molecules, which was not conducive to improving their emulsifying properties.

CONCLUSION

Optimal HSH speed was achieved at 14 500 rpm to modify MPs' emulsifying and structural properties under low-fatconditions. © 2019 Society of Chemical Industry.

Potential of recovered proteins from invasive green crabs (Carcinus maenas) as a functional food ingredient

BACKGROUND

Invasive green crabs contain high-quality proteins that have potential as functional ingredients in formulated foods. This study evaluated the functional properties and compositional characteristics of green crab proteins recovered by isoelectric solubilization/precipitation (ISP).

RESULTS

Mechanically separated green crab mince (control) was solubilized at pH 2 (PP2) and pH 10 (PP10), then proteins were precipitated at pH 5.5 and subsequently dried. Yield of recovered protein powder was approximately 1.5 times higher for PP2 than for PP10. Compared with the control (230 g kg^-1 ), ash content was reduced in PP2 (54 g kg^-1 ) and PP10 (23 g kg^-1 ) samples. PP2 contained predominantly large-molecular-weight proteins, while small-molecular-weight proteins were distributed in PP10. With regard to functional properties, at pH 7 and 8, solubility of PP10 was significantly higher than that of PP2. At pH 7.5, PP10 exhibited significantly higher emulsifying activity (1482 m² g^-1 ) than PP2 (858 m² g^-1 ) and the control (958 m² g^-1 ). PP2 showed statistically higher gelation activity and had higher L* value than PP10 and the control.

CONCLUSION

The results indicate that recovered green crab proteins have functional properties potentially useful for formulated foods, and that these functional properties can be modified by the solubilization pH during the recovery process. © 2018 Society of Chemical Industry.

Catch muscle myorod modulates ATPase activity of Myosin in a phosphorylation-dependent way

Myorod is expressed exclusively in molluscan catch muscle and localizes on the surface of thick filaments together with twitchin and myosin. Myorod is an alternatively spliced product of the myosin heavy-chain gene that contains the C-terminal rod part of myosin and a unique N-terminal domain. The unique domain is a target for phosphorylation by gizzard smooth myosin light chain kinase (smMLCK) and, perhaps, molluscan twitchin, which contains a MLCK-like domain. To elucidate the role of myorod and its phosphorylation in the catch muscle, the effect of chromatographically purified myorod on the actin-activated Mg2+-ATPase activity of myosin was studied. We found that phosphorylation at the N-terminus of myorod potentiated the actin-activated Mg2+-ATPase activity of mussel and rabbit myosins. This potentiation occurred only if myorod was phosphorylated and introduced into the ATPase assay as a co-filament with myosin. We suggest that myorod could be related to the catch state, a function specific to molluscan muscle.

Stable isotope labeling for proteomic analysis of tissues in mouse

Since the first metabolic labeling experiments with stable isotopes beginning of the last century, several approaches were pursued to monitor protein dynamics in living animals. Today, almost all model organisms from bacteria to rodents can be fully labeled with SILAC (stable isotope labeling of amino acids in cell culture) amino acids. The development of special media and diets containing the labeled amino acids provides an efficient way to metabolically label prokaryotic and eukaryotic organisms. Preferentially, the essential amino acid lysine ((13)C6-lysine) is used to label mice (Mus musculus) and after one generation the natural isotope is fully replaced by the stable (13)C6-lysine isotope. So far, the SILAC mouse approach has been used to analyze several transgenic and knockout mouse models. Spike-in of labeled proteins into non-labeled samples provides an accurate relative protein quantification method without any chemical modification. Here we describe how to establish a SILAC mouse colony and describe the analysis of skeletal muscle tissue with different metabolic and contractile profiles.

Purification and characterization of antioxidative peptides from round scad (Decapterus maruadsi) muscle protein hydrolysate

Muscle protein from round scad (Decapterus maruadsi) was hydrolyzed with five commercial proteases, namely, Alcalase, neutral protease, papain, pepsin, and trypsin. Round scad hydrolysate (RSH) prepared with Alcalase demonstrated high antioxidative activity. After ultrafiltration, RSH-III fraction (MW<5kDa) exhibited the strongest activity. Then, RSH-III was purified by gel filtration chromatography (Sephadex G-15) and separated into four fractions (A, B, C, and D), of which fraction B showed the highest antioxidative activity and was further purified using reverse-phase high-performance liquid chromatography twice. The purified peptides were identified as His-Asp-His-Pro-Val-Cys (706.8Da) and His-Glu-Lys-Val-Cys (614.7Da) by matrix-assisted laser desorption ionization time-of-flight/time-of-flight mass spectrometry. Subsequently, the identified peptides were synthesized, and their antioxidative activities were verified. Results indicated that the two novel peptides isolated from round scad muscle protein can be developed into antioxidative ingredients in functional foods.

20 years from NCX purification and cloning: milestones

The Na(+)/Ca(2+) exchanger protein was first isolated from cardiac sarcolemma in 1988 and cloned in 1990. This allowed study of Na(+)/Ca(2+) exchange at the molecular level to begin. I will review the story leading to the cloning of NCX and the research that resulted from this event. This will include structure-function studies such as determination of the numbers of transmembrane segments and topological arrangement. Information on ion transport sites has been gathered from site-directed mutagenesis. The regions involved in Ca(2+) regulation have been identified, analyzed, and crystallized.We have also generated genetically altered mice to study the role of NCX in the myocardium. Of special interest are mice with atrial- or ventricular-specific KO of NCX that reveal new information on the role of NCX in excitation-contraction coupling and in cardiac pacemaker activity.

Autoantibodies produced at the site of tissue damage provide evidence of humoral autoimmunity in inclusion body myositis

Inclusion body myositis (IBM) belongs to a group of muscle diseases known as the inflammatory myopathies. The presence of antibody-secreting plasma cells in IBM muscle implicates the humoral immune response in this disease. However, whether the humoral immune response actively contributes to IBM pathology has not been established. We sought to investigate whether the humoral immune response in IBM both in the periphery and at the site of tissue damage was directed towards self-antigens. Peripheral autoantibodies present in IBM serum but not control serum recognized self-antigens in both muscle tissue and human-derived cell lines. To study the humoral immune response at the site of tissue damage in IBM patients, we isolated single plasma cells directly from IBM-derived muscle tissue sections and from these cells, reconstructed a series of recombinant immunoglobulins (rIgG). These rIgG, each representing a single muscle-associated plasma cell, were examined for reactivity to self-antigens. Both, flow cytometry and immunoblotting revealed that these rIgG recognized antigens expressed by cell lines and in muscle tissue homogenates. Using a mass spectrometry-based approach, Desmin, a major intermediate filament protein, expressed abundantly in muscle tissue, was identified as the target of one IBM muscle-derived rIgG. Collectively, these data support the view that IBM includes a humoral immune response in both the periphery and at the site of tissue damage that is directed towards self-antigens.

Optimization of hydrolysis conditions for the production of angiotensin-I converting enzyme-inhibitory peptides and isolation of a novel peptide from lizard fish (Saurida elongata) muscle protein hydrolysate

Lizard fish (Saurida elongata) muscle protein was hydrolyzed using neutral protease to produce protein hydrolysate (LFPH), and the hydrolysis conditions were investigated using response-surface methodology. The optimum conditions for producing peptides with the highest angiotensin-I converting enzyme (ACE)-inhibitory activity were the following: enzyme-to-substrate ratio of 10,000 U/g, temperature of 48 °C, pH 7.0, and hydrolysis time of 2 h. Under these conditions, the ACE-inhibitory activity of LFPH and the degree of hydrolysis were 84% and 24%, respectively. A novel ACE-inhibitory peptide was isolated from LFPH using ultrafiltration, Sephadex G-15, and high-performance liquid chromatography. The amino acid sequence of the ACE-inhibitory peptide was identified as Ser-Pro-Arg-Cys-Arg (SPRCR), and its IC₅₀ was 41 ± 1 µM.

2D DIGE analysis of protein extracts from muscle tissue

2D DIGE, two-dimensional difference gel electrophoresis, is a technology used to study the protein expression on two-dimensional gels. Protein samples are labeled with different color fluorescent dyes designed not to affect the relative migration of proteins during electrophoresis. Here, we describe the practical procedures necessary to perform a 2D DIGE experiment for a muscle tissue protein extract followed by CyDye DIGE fluors minimal labeling and the analysis of 2D DIGE gels for the assessment of quantitative differences.

Protein solubilization: attend to the choice of lysis buffer

The efficient extraction of proteins of interest from cells and tissues is not always straightforward. In this process, the use of the optimal lysis buffer for protein solubilization should be considered. Here we demonstrate the use of a urea/thiourea lysis buffer, based on O'Farrell's buffer, and compare its effectiveness for solubilization of proteins from smooth muscle with the often utilized RIPA lysis buffer.

Gut CaVP is an innate immune protein against bacterial challenge in amphioxus Branchiostoma belcheri

The importance of calcium-binding proteins in immune response of vertebrates is determined, but whether they have the role in invertebrates is largely unknown. In the present study, phylogenetic analysis indicated that calcium vector protein (CaVP), a protein unique to amphioxus, shared 68% similarity in amino acid sequence with human and mouse calmodulin (CaM). CaVP cDNA was cloned into a bacterial vector pET-32a, and its His-tagged fusion protein was produced in Eschherichia coli cells (BL21). The recombinant CaVP was purified by Ni-NTA column and SDS-PAGE, and then utilized for antibody preparing. The prepared antibodies could recognize amphioxus CaVP with high specificity. Further analysis by Western blotting showed that CaVP was detected in muscle and humoral fluid of normal animals and appeared in gut of bacterial immunized or challenged amphioxus. Interestingly, gut CaVP was significantly higher in a healthy sub-group than a wounded sub-group post bacterial challenge. This response was detected strongly in immunization and challenge by the same Gram-negative bacterium Vibro parahaemolyticus and weakly in immunization by V. parahaemolyticus and then challenge by Gram-negative Aeromonas hydrophila, whereas no any feedback was found in immunization by V. parahaemolyticus and challenge by Gram-positive Staphylococcus aureus. These findings indicate the importance of gut CaVP in response to bacterial challenge.

[Construction of eukaryotic fusion expression vectors of LSDP5 and cellular localization]

AIM

To construct the eukaryotic fusion expression vectors and localization of (lipid storage droplet protein 5, LSDP5) in COS7 cells.

METHODS

Eukaryotic expression plasmid pCMV5-HA was digested with Nde I and BamH I and pMD18-LSDP5 plasmid was digested with Bgl II and Nde I. Full length LSDP5 was subcloned into pCMV5-HA. After confirmed by restriction enzyme digestion analysis and sequencing, the plasmid pCMV5-HA-LSDP5 was transfected into COS7 cells using Lipofectamine 2000 and the expression and localization of the fusion protein was detected by fluorescent microscope.

RESULTS

Restriction digestions and sequencing assays showed that the recombinant plasmid of pCMV5-HA-LSDP5 was successfully constructed and the fusion proteins were detected in cytoplasm and were targeted to the surfaces of lipid droplets visualized by Bodipy 493/503 in COS7 cells.

CONCLUSION

The recombined plasmid pCMV5-HA-LSDP5 expressing the fusion protein of LSDP5 and HA-tagged is successfully constructed and the fusion protein distributes in cytoplasm and is co-localized with lipid droplets.

Nuclear titin interacts with histones

BACKGROUND

Titin is a giant muscle protein that is responsible for the elasticity of muscle and may also function as a molecular scaffold for myofibrillar assembly. However, its presence in the nucleus remains elusive.

METHODS

Nuclear titin was extracted with 0.15 M sodium phosphate buffer containing 0.3 M NaCl, followed by ammonium sulfate fractionation and gel filtration column chromatography. The proteins not separable from titin were subjected to mass spectrometry (MS) and MS/MS analyses.

RESULTS

This purification procedure removed almost all impurities except three low molecular weight proteins (12-15 kDa). These proteins were not separated from titin through various types of column chromatography, indicating their strong interaction with nuclear titin. These proteins were identified as histones H2A, H3 and H4 by MS and MS/MS analyses.

CONCLUSION

The existence of titin in the nucleus was confirmed by obtaining purified titin from the nucleus. Furthermore, nuclear titin exhibited strong interaction with histones H2A, H3 and H4, suggesting its role as a chromosome scaffold.

On a basic 31 kDa muscle membrane protein in cattle and pig, presumably equivalent to the class II antigen associated p31 molecule

In a recent paper we gave evidence by two-dimensional electrophoresis that, in man, the class II antigen associated glycoprotein p31 (also called Ii, In, M1, DR gamma, XM1) is expressed not only in the membranes of B lymphocytes but also in those of muscle, liver and brain. It can therefore be assumed that the p31 is not really associated with the human class II antigens but is a ubiquitous molecule. Here we demonstrate for the first time that the muscle membranes of cattle and pig contain corresponding polypeptides, with a molecular weight of about 31 kDa and an isoelectric point around 7.5, which comigrate in two-dimensional electrophoresis with p31 derived from the human muscle. Thus, in cattle and pig too, these proteins seem to be equivalent to the class II antigen associated p31, showing a tissue distribution wider than observed up to now. The molecules can be concentrated by ion-exchange chromatography.

Biochemical properties of gastrokine-1 purified from chicken gizzard smooth muscle

The potential role and function of gastrokine-1 (GNK1) in smooth muscle cells is investigated in this work by first establishing a preparative protocol to obtain this native protein from freshly dissected chicken gizzard. Some unexpected biochemical properties of gastrokine-1 were deduced by producing specific polyclonal antibody against the purified protein. We focused on the F-actin interaction with gastrokine-1 and the potential role and function in smooth muscle contractile properties.

Background

GNK1 is thought to provide mucosal protection in the superficial gastric epithelium. However, the actual role of gastrokine-1 with regards to its known decreased expression in gastric cancer is still unknown. Recently, trefoil factors (TFF) were reported to have important roles in gastric epithelial regeneration and cell turnover, and could be involved in GNK1 interactions. The aim of this study was to evaluate the role and function of GNK1 in smooth muscle cells.

Methodology/Principal Findings

From fresh chicken gizzard smooth muscle, an original purification procedure was used to purify a heat soluble 20 kDa protein that was sequenced and found to correspond to the gastrokine-1 protein sequence containing one BRICHOS domain and at least two or possibly three transmembrane regions. The purified protein was used to produce polyclonal antibody and highlighted the smooth muscle cell distribution and F-actin association of GNK1 through a few different methods.

Conclusion/Significance

Altogether our data illustrate a broader distribution of gastrokine-1 in smooth muscle than only in the gastrointestinal epithelium, and the specific interaction with F-actin highlights and suggests a new role and function of GNK1 within smooth muscle cells. A potential role via TFF interaction in cell-cell adhesion and assembly of actin stress fibres is discussed.

In vivo measurement of synthesis rate of individual skeletal muscle mitochondrial proteins

Skeletal muscle mitochondrial dysfunction occurs in many conditions including aging and insulin resistance, but the molecular pathways of the mitochondrial dysfunction remain unclear. Presently, no methodologies are available to measure synthesis rates of individual mitochondrial proteins, which limits our ability to fully understand the translational regulation of gene transcripts. Here, we report a methodology to measure synthesis rates of multiple muscle mitochondrial proteins, which, along with large-scale measurements of mitochondrial gene transcripts and protein concentrations, will enable us to determine whether mitochondrial alteration is due to transcriptional or translational changes. The methodology involves in vivo labeling of muscle proteins with l-[ring-(13)C(6)]phenylalanine, protein purification by two-dimensional gel electrophoresis of muscle mitochondrial fraction, and protein identification and stable isotope abundance measurements by tandem mass spectrometry. Synthesis rates of 68 mitochondrial and 23 nonmitochondrial proteins from skeletal muscle mitochondrial fraction showed a 10-fold range, with the lowest rate for a structural protein such as myosin heavy chain (0.16 +/- 0.04%/h) and the highest for a mitochondrial protein such as dihydrolipoamide branched chain transacylase E2 (1.5 +/- 0.42%/h). This method offers an opportunity to better define the translational regulation of proteins in skeletal muscle or other tissues.

Identification of transgelin as a potential novel biomarker for gastric adenocarcinoma based on proteomics technology

PURPOSE

To find a biomarker for gastric adenocarcinomas (GA).

METHODS

Ten protein expression profiles of GA and paired non-neoplastic mucosa tissues were analyzed by two-dimensional gel electrophoresis. Forty-two protein spots that were differentially expressed by twofold or greater between cancer and normal mucosa tissue were excised and identified by MALDI-TOF/TOF MS. One of the over-expressed proteins identified in GA was transgelin, which was chosen for further verification by immunohistochemistry and western blotting.

RESULTS

Forty-two distinct proteins that were differentially expressed at least twofold between the tissues were identified. Expression of 29 of these proteins was decreased (ratio >or= 2, P < 0.01), including adenosine deaminase; and 13 proteins displayed over-expression in cancer tissue (ratio >or= 2, P < 0.01), including transgelin. The results of immunohistochemistry confirmed that transgelin was indeed over-expressed in 22 cases of GA (22/41, 53.66%), with strong cytoplasmic staining in cancer cells of positive samples, this was absent in most paired non-neoplastic mucosa cells or gastric ulcer tissues (n = 20). Transgelin was found over-expressed in 21 samples of cancer tissue (21/41, 51.22%) when detected by western blot.

CONCLUSION

This work demonstrates that differentially expressed proteins can be identified by proteomics technology combined with immunohistochemistry and western blot analyses. We have identified one such protein, transgelin, as a novel biomarker for GA.

Protein recovery from rainbow trout (Oncorhynchus mykiss) processing byproducts via isoelectric solubilization/precipitation and its gelation properties as affected by functional additives

Solubility of rainbow trout proteins was determined between pH 1.5 and 13.0 and various ionic strengths (IS). Minimum solubility occurred at pH 5.5; however, when IS = 0.2, the minimum solubility shifted toward more acidic pH. Isoelectric solubilization/precipitation was applied to trout processing byproducts (fish meat left over on bones, head, skin, etc.), resulting in protein recovery yields (Kjeldahl, dry basis) between 77.7% and 89.0%, depending of the pH used for solubilization and precipitation. The recovered protein contained 1.4-2.1% ash (dry basis), while the trout processing byproducts (i.e., starting material) 13.9%. Typical boneless and skinless trout fillets contain 5.5% ash, and therefore, the isoelectric solubilization/precipitation effectively removed impurities such as bones, scales, skin, etc., from the trout processing byproducts. The recovered proteins retained gel-forming ability as assessed with dynamic rheology, torsion test, and texture profile analysis (TPA). However, the recovered proteins failed to gel unless beef plasma protein (BPP) was added. Even with BPP, the recovered protein showed some proteolysis between 40 and 55 degrees C. Addition of potato starch, transglutaminase, and phosphate to the recovered proteins resulted in good texture of trout gels as confirmed by torsion test and TPA. Higher ( P < 0.05) shear stress and strain were measured for gels developed from basic pH treatments than the acidic counterparts. However, proteins recovered from acidic treatments had higher ( P < 0.05) lipid content than the basic treatments. This is probably why the gels from acidic treatments were whiter ( L* - 3 b*) ( P < 0.05) than those from the basic ones. Our study demonstrates that functional proteins can be efficiently recovered from low-value fish processing byproducts using isoelectric solubilization/precipitation and subsequently be used in value-added human foods.

Antihypertensive effect of angiotensin i converting enzyme-inhibitory peptide from hydrolysates of Bigeye tuna dark muscle, Thunnus obesus

Angiotensin I converting enzyme (ACE) inhibitory peptide was isolated from tuna dark muscle hydrolysate prepared by alcalase, neutrase, pepsin, papain, alpha-chymotrypsin, and trypsin, respectively. Among hydrolysates, the pepsin-derived hydrolysate exhibited the highest ACE I inhibitory activity versus those of other enzyme hydrolysates. The structure of the peptide was identified to be Trp-Pro-Glu-Ala-Ala-Glu-Leu-Met-Met-Glu-Val-Asp-Pro (molecular weight 1581 Da) by time of flight mass spectrometry/mass spectrometry analysis, and the IC 50 value of the peptide was 21.6 microM. The Lineweaver-Burk plots revealed that the peptide acts as a noncompetitive inhibitor, and the inhibitor constant ( K i) was calculated as 26.6 microM using the secondary plots. The peptide had an antihypertensive effect according to the time-course measurement after oral administration to spontaneously hypertensive rats. Maximal reduction was detected 3 h after oral administration at a dose of 10 mg/kg of body weight. These results suggest that the peptide derived from tuna dark muscle would be a beneficial ingredient for functional food or pharmaceuticals against hypertension and its related diseases.

Combination of peptide OFFGEL fractionation and label-free quantitation facilitated proteomics profiling of extraocular muscle

Several label-free quantitation strategies have been introduced that obliterate the need for expensive isotopically labeled molecules. However label-free approaches have considerably higher demands in respect of repeatability of sample preparation and fractionation than multiplexing isotope labeling-based strategies. OFFGEL fractionation promises the necessary separation efficiency and repeatability. To test this platform, 12-fraction peptide OFFGEL electrophoresis and online reversed-phase LC connected to a quadrupole TOF mass spectrometer were used to determine differences of the physiological, pathological and biochemical distinct extraocular muscle allotype in comparison to hind-limb muscle. Close to 70% of the peptides separated by OFFGEL electrophoresis were detected only in a single fraction. To determine the separation repeatability of four samples, we compared the ion volumes of multiple peptides deriving from the thick filament-associated protein titin over several fractions and determined a coefficient of variation below 20%. Of the 474 proteins identified, 61 proteins were differently expressed between the two muscle allotypes and were involved in metabolism, muscle contraction, stress response, or gene expression. Several expression differences were validated using immunohistochemistry and Western blot analysis. We therefore consider peptide OFFGEL fractionation an effective and efficient addition to our label-free quantitative proteomics workflow.

Two LIM domain proteins and UNC-96 link UNC-97/pinch to myosin thick filaments in Caenorhabditis elegans muscle

By yeast two-hybrid screening, we found three novel interactors (UNC-95, LIM-8, and LIM-9) for UNC-97/PINCH in Caenorhabditis elegans. All three proteins contain LIM domains that are required for binding. Among the three interactors, LIM-8 and LIM-9 also bind to UNC-96, a component of sarcomeric M-lines. UNC-96 and LIM-8 also bind to the C-terminal portion of a myosin heavy chain (MHC), MHC A, which resides in the middle of thick filaments in the proximity of M-lines. All interactions identified by yeast two-hybrid assays were confirmed by in vitro binding assays using purified proteins. All three novel UNC-97 interactors are expressed in body wall muscle and by antibodies localize to M-lines. Either a decreased or an increased dosage of UNC-96 results in disorganization of thick filaments. Our previous studies showed that UNC-98, a C2H2 Zn finger protein, acts as a linkage between UNC-97, an integrin-associated protein, and MHC A in myosin thick filaments. In this study, we demonstrate another mechanism by which this linkage occurs: from UNC-97 through LIM-8 or LIM-9/UNC-96 to myosin.

Effect of chitosan and chitin on the separation of membranes from proteins solubilized by pH shifts using cod (Gadus morhua)

Studies with isolated membranes and isolated membranes suspended in muscle proteins solubilized at pH 3 showed that mixing chitosan and membranes at this low pH followed by a pH adjustment to 10.5 could sediment membranes effectively at 4000 g. In the solubilized muscle homogenate, the effectiveness of membrane removal by chitosan at 4000 g for 15 min was molecular weight dependent. About 80% of the phospholipids and 28% of proteins were sedimented from solubilized muscle homogenate by mixing muscle homogenate (10 g of muscle tissue homogenized with 90 mL of distilled water) with 10 mL of MW 310-375 k chitosan (10 mg/mL in 0.1 N HCl) before solubilizing it at pH 10.5, whereas 55% of the phospholipids and 12% of proteins were sedimented by mixing muscle homogenate with the MW 310-375 k chitosan before solubilizing the homogenate at pH 3. Low molecular weight chitosans (at MW 1k or 33k) showed little effect on membrane sedimentation under the same conditions. Chitin was not useful for removing membranes at either pH 3 or 10.5, whether added before or after pH adjustment.

Repeated bout effect on the cytoskeletal proteins titin, desmin, and dystrophin in rat skeletal muscle

The aim of this study was to evaluate the effect of repeated bouts of exercise on the cytoskeletal proteins titin, desmin, and dystrophin. Rats were made to run downhill for 90 min 1 or 5 times separated by 14 days. Samples were taken from quadriceps femoris muscle 3, 48, 96 h and 50 days after the last exercise session and detected by quantitative PCR, histochemical stainings, and western blot analyses. Histopathological changes in titin, desmin, and dystophin stainings, an increase in beta-glucuronidase activity (a quantitative indicator of muscle damage), a significant decrease in the relative content of dystrophin, and intramyocellular Evans blue staining (signs of changes in sarcolemmal permeability) observed after one exercise session were attenuated after 5 exercise sessions. Titin mRNA level was not increased after the initial exercise session but was increased after the fifth session. Desmin and dystrophin mRNA levels were increased after the first and fifth sessions with desmin showing a smaller increase after the fifth session compared to the first session. Prior exercise induces adaptation that protects the sarcolemma as well as subsarcolemmal, intermediate filament, and sarcomeric proteins against disruption. Changes in mRNA levels of titin, desmin, and dystophin after an acute exercise session obviously reflect the need of these proteins in the repair process following damage. After five sessions increase in mRNA of studied proteins suggest a strong involvement in continuing adaptation to the increased exercise.

A comparative proteome analysis of human metaphase chromosomes isolated from two different cell lines reveals a set of conserved chromosome-associated proteins

A comparative proteome analysis of human metaphase chromosomes between a typical epithelial-like cell, HeLa S3, and a lymphoma-type cell, BALL-1, was performed. One-dimensional (1-D) SDS-PAGE and radical-free and highly reducing two-dimensional electrophoresis (RFHR 2-DE) detected more than 200 proteins from chromosomes isolated from HeLa S3 cells, among which 189 proteins were identified by mass spectrometry (MS). Consistent with our recent four-layer structural model of a metaphase chromosome, all the identified proteins were grouped into four distinct levels of abundance. Both HeLa S3 and BALL-1 chromosomes contained specific sets of abundant chromosome structural and peripheral proteins in addition to less abundant chromosome coating proteins (CCPs). Furthermore, titin array analysis and a proteome analysis of the ultra-high molecular mass region indicated an absence of titin with their molecular weight (MW) more than 1000 kDa. Consequently, the present proteome analyses together with previous information on chromosome proteins provide the comprehensive list of proteins essential for the metaphase chromosome architecture.

Proteomic profiling and identification of cofilin responding to oxidative stress in vascular smooth muscle

We used 2-DE and MALDI-TOF/TOF to identify proteins of vascular smooth muscle cells whose expression was or was not altered by exposure to 500 microM H2O2 for 30 min. We detected more than 800 proteins on silver-stained gels of whole protein extracts from rat aortic smooth muscle strips. Of these proteins, 135 clearly unaffected and 19 having levels altered by exposure to H2O2 were identified. Protein characterization revealed that the most prominent vascular smooth muscle proteins were those with antioxidant, cytoskeletal structure, or muscle contraction. In addition, cofilin, an isoform of the actin depolymerizing factor family, shifted to its basic site on the 2-DE gel as a result of H2O2 treatment. In Western blot analysis of proteins from A7r5 aortic smooth muscle cells, the phosphorylation, but not the expression, of cofilin was decreased by H2O2 in a dose-dependent manner. The H2O2-induced dephosphorylation of cofilin and apoptosis was inhibited by Na3VO4, an inhibitor of protein tyrosine phosphatase (PTP). These results suggest that cofilin is one of the proteins regulated by H2O2 treatment in vascular smooth muscle, and has an important role in the induction of vascular apoptosis through PTP-dependent mechanisms.

Crystallization and Preliminary Crystallographic Analysis of Transgelin

Transgelin was solubly expressed in E. coli. Crystals of transgelin have been grown at 291K using sodium formate or PEG-4000 as precipitants. X-ray diffraction by the crystal extends to 2.3 A resolution. The crystal belongs to the space group P2(1), with the unit cell parameters a=39.3, b=61.9, c=56.0 A and beta=90.2 degrees .

Identification of secreted proteins during skeletal muscle development

The differentiation program of skeletal muscle cells is exquisitely sensitive to secreted proteins. We developed a strategy to maximize the discovery of secreted proteins, using mass spectrometry-based proteomics, from cultured muscle cells, C2C12, grown in a serum-free medium. This strategy led to the identification of 80 nonredundant proteins, of which 27 were secretory proteins that were identified with a minimum of two tryptic peptides. A number of the identified secretory proteins are involved in extracellular matrix remodeling, cellular proliferation, migration, and signaling. A putative network of proteins involving matrix metalloproteinase 2, SPARC, and cystatin C that all interact with TGFbeta signaling has been postulated to contribute toward a functional role in the myogenic differentiation program.

p38-MAPK induced dephosphorylation of alpha-tropomyosin is associated with depression of myocardial sarcomeric tension and ATPase activity

Our objective in work presented here was to understand the mechanisms by which activated p38alpha MAPK depresses myocardial contractility. To test the hypothesis that activation of p38 MAPK directly influences sarcomeric function, we used transgenic mouse models with hearts in which p38 MAPK was constitutively turned on by an upstream activator (MKK6bE). These hearts demonstrated a significant depression in ejection fraction after induction of the transgene. We also studied hearts of mice expressing a dominant negative p38alpha MAPK. Simultaneous determination of tension and ATPase activity of detergent-skinned fiber bundles from left ventricular papillary muscle demonstrated a significant inhibition of both maximum tension and ATPase activity in the transgenic-MKK6bE hearts. Fibers from hearts expressing dominant negative p38alpha MAPK demonstrated no significant change in tension or ATPase activity. There were no significant changes in phosphorylation level of troponin-T3 and troponin-T4, or myosin light chain 2. However, compared with controls, there was a significant depression in levels of phosphorylation of alpha-tropomyosin and troponin I in fiber bundles from transgenic-MKK6bE hearts, but not from dominant negative p38alpha MAPK hearts. Our experiments also showed that p38alpha MAPK colocalizes with alpha-actinin at the Z-disc and complexes with protein phosphatases (PP2alpha, PP2beta). These data are the first to indicate that chronic activation of p38alpha MAPK directly depresses sarcomeric function in association with decreased phosphorylation of alpha-tropomyosin.

Quantitative proteomics profiling of sarcomere associated proteins in limb and extraocular muscle allotypes

The sarcomere is the major structural and functional unit of striated muscle. Approximately 65 different proteins have been associated with the sarcomere, and their exact composition defines the speed, endurance, and biology of each individual muscle. Past analyses relied heavily on electrophoretic and immunohistochemical techniques, which only allow the analysis of a small fraction of proteins at a time. Here we introduce a quantitative label-free, shotgun proteomics approach to differentially quantitate sarcomeric proteins from microgram quantities of muscle tissue in a fast and reliable manner by liquid chromatography and mass spectrometry. The high sequence similarity of some sarcomeric proteins poses a problem for shotgun proteomics because of limitations in subsequent database search algorithms in the exclusive assignment of peptides to specific isoforms. Therefore multiple sequence alignments were generated to improve the identification of isoform specific peptides. This methodology was used to compare the sarcomeric proteome of the extraocular muscle allotype to limb muscle. Extraocular muscles are a unique group of highly specialized muscles with distinct biochemical, physiological, and pathological properties. We were able to quantitate 40 sarcomeric proteins; although the basic sarcomeric proteins in extraocular muscle are similar to those in limb muscle, key proteins stabilizing the connection of the Z-bands to thin filaments and the costamere are augmented in extraocular muscle and may represent an adaptation to the eccentric contractions known to normally occur during eye movements. Furthermore, a number of changes are seen that closely relate to the unique nature of extraocular muscle.

Dissociated flexor digitorum brevis myofiber culture system—A more mature muscle culture system

Considerable knowledge regarding skeletal muscle physiology and disease has been gleaned from cultured myoblastic cell lines or isolated primary myoblasts. Such muscle cultures can be induced to differentiate into multinucleated myotubes that become striated. However they in general do not fully mature and therefore do not model mature muscle. Contrastingly, fresh and cultured dissociated adult mouse flexor digitorum brevis (FDB) myofibers have been studied for many years. We aimed to investigate the possibility of using the FDB myofiber culture system for drug screening and thus long-term cultures of enzymatically dissociated FDB myofibers were established in 96-well plates. Ca2+ handling experiments were used to investigate the functional state of the myofibers. Imaging of intracellular Ca2+ during electric field stimulation revealed that calcium handling was maintained throughout the culture period of at least 8 days. Western blot and immunostaining analysis showed that the FDB cultures maintained expression of mature proteins throughout the culture period, including alpha-sarcoglycan, dystrophin, fast myosin heavy chain and skeletal muscle alpha-actin. The high levels of the fetal proteins cardiac alpha-actin and utrophin, seen in cultured C2C12 myotubes, were absent in the FDB cultures. The expression of developmentally mature proteins and the absence of fetal proteins, in addition to the maintenance of normal calcium handling, highlights the FDB culture system as a more mature and perhaps more relevant culture system for the study of adult skeletal muscle function. Moreover, it may be a useful system for screening therapeutic agents for the treatment of skeletal muscle disorders.

Isolation of Intracellular Proteinase Inhibitors Derived from Designed Ankyrin Repeat Proteins by Genetic Screening

The specific intracellular inhibition of protein activity at the protein level is a highly valuable tool for the validation or modulation of cellular processes. We demonstrate here the use of designed ankyrin repeat proteins (DARPins) as tailor-made intracellular proteinase inhibitors. Site-specific proteolytic processing plays a critical role in the regulation of many biological processes, ranging from basic cellular functions to the propagation of viruses. The NIa(pro) proteinase of tobacco etch virus, a major plant pathogen, can be functionally expressed in Escherichia coli without harming the bacterium. To identify inhibitors of this proteinase, we first selected binders to it from combinatorial libraries of DARPins and tested this pool with a novel in vivo screen for proteinase inhibition. For this purpose, a hybrid protein consisting of the omega subunit of E. coli RNA polymerase was covalently fused to a DNA-binding protein, the lambdacI repressor, containing an NIa(pro) cleavage site in the linker between the two proteins. Thus, this transcriptional activator is inactivated by site-specific proteolytic cleavage, and inhibitors of this cleavage can be identified by the reconstitution of transcription of a reporter gene. Following this two-step approach of selection and screening, we could rapidly isolate NIa(pro) proteinase inhibitors active inside the cell from highly diverse combinatorial DARPin libraries. These findings underline the great potential of DARPins for modulation of protein functionality in the intracellular space. In addition, our novel genetic screen can help to select and identify tailor-made proteinase inhibitors based on other protein scaffolds or even on low molecular weight compounds.

Phosphorylation of myorod (catchin) by kinases tightly associated to molluscan and vertebrate smooth muscle myosins

Myorod, also known as catchin, a newly discovered component of molluscan smooth muscle thick filaments, is an alternative product of the myosin heavy chain gene. It contains a C-terminal rod part that is identical to that part of myosin and a unique N-terminal domain that is very small relative to the myosin head domain. The role of myorod in contraction or relaxation of this muscle type is unknown. In the present study we demonstrated that myorod was phosphorylated not only by a kinase endogenous to molluscan myosin and twitchin but also to vertebrate smooth muscle myosin light chain kinase (MLCK). The rates and maximal levels of phosphorylation were up to threefold higher than those observed by protein kinase A with clear optima at the physiological salt concentrations. Using a mild digestion with chymotrypsin we isolated an 11 kDa phosphopeptide and showed that the phosphorylation site was located at the N-terminal domain of myorod at Thr 141 position. The sequence around this site exhibited a high degree of similarity to that expected for the substrate recognition site of MLCK. The phosphorylation rates strongly depended on the ionic conditions indicating that this site could be readily sterically blocked during myorod polymerization. Another component of the thick filaments involved in regulation of the catch state, twitchin, was phosphorylated by MLCK and exhibited endogenous myorod kinase and MLCK activities. A possible role of these phosphorylation reactions in the regulation of molluscan smooth muscles is discussed.

[Expression, purification and antibody preparation of recombinant human SM22alpha]

AIM

The recombinant human smooth muscle 22 alpha (SM22alpha) was expressed by using Pichia pastoris.

METHODS

Using pGEM3z-SM22alpha as the template, SM22alpha coding region was amplified by PCR, and was inserted the expression vector pPIC9. Then the recombinant plasmid pPIC9-SM22alpha was transfected into Pichia pastoris. The products induced by methanol were precipitated by ammonium sulfate, then CM-cellulose chromatography was performed for SM22alpha. Polyclonal antibody against SM22alpha was produced by immunizing a rabbit with purified recombinant SM22alpha.

RESULTS

The positive clone with SM22alpha got high output at 84 hours after induction by methanol. The SM22alpha prepared by ammonium sulfate fractionation and chromatographic separation showed a single band whose apparent molecular weight was 22 kD on SDS-PAGE. Polyclonal antibody against SM22alpha could detect the SM22alpha expression in human or rat vascular walls.

CONCLUSION

High-level expression of SM22alpha is successfully achieved in Pichia pastoris. Antibody against SM22alpha can be used to explore the function of SM22alpha.

The structural principles of multidomain organization of the giant polypeptide chain of the muscle titin protein: SAXS/WAXS studies during the stretching of oriented titin fibres

Elasticity of titin is a key parameter that determines the mechanical properties of muscle. These include reversibility, i.e., the muscle's capacity to change its length many-fold and return to its original state, and the transduction of passive tension generated by the stretched muscle. The morphology and elastic properties of oriented fibres of titin molecules were studied using SAXS and WAXS (small- and wide-angle X-ray scattering, respectively) and mechanical techniques. We succeeded in obtaining oriented filaments of purified titin suitable for diffraction measurements. Our X-ray data suggest a model of titin as a nanoscale, morphological, and aperiodical array of rigid Ig- and Fn3-type domains covalently connected by conformationally variable short loops. The line group symmetry of the model can be defined as SM with axial translation tau(infinity). Both tension transduction and high elasticity of titin can be explained in terms of crystalline polymer physics. Titin stretching experiments show that each individual titin macromolecule can adopt a novel two-phase state within the fibre. Conversion between high elasticity and strength can be explained as a phase transition under external tension. In the terms of the concept of orientational melting the origin of the functional heterogeneity along the titin strand becomes interpretable.

Proteomic dataset of mouse aortic smooth muscle cells

In an accompanying study (in this issue, DOI 10.1002/pmic.200402044), we have characterised the proteome of Sca-1(+) progenitor cells, which may function as precursors of vascular smooth muscle cells (SMCs). In the present study, we have analysed and mapped protein expression in aortic SMCs of mice, using 2-DE, MALDI-TOF MS and MS/MS. The 2-D system comprised a non-linear immobilised pH 3-10 gradient in the first dimension (separating proteins with pI values of pH 3-10), and 12%T SDS-PAGE in the second dimension (separating proteins in the range 15,000-150,000 Da). Of the 2400 spots visualised, a subset of 267 protein spots was analysed, with 235 protein spots being identified corresponding to 154 unique proteins. The data presented here are the first map of aortic SMCs and the most extensive analysis of SMC proteins published so far. This valuable tool should provide a basis for comparative studies of protein expression in vascular smooth muscle of transgenic mice and is available on our website hhtp://www.vascular-proteomics.com.

Catalytic subunit of cAMP-dependent protein kinase from a catch muscle of the bivalve mollusk Mytilus galloprovincialis: purification, characterization, and phosphorylation of muscle proteins

cAMP-dependent protein kinase (PKA) plays a crucial role in the release of the catch state of molluskan muscles, but the nature of the enzyme in such tissues is unknown. In this paper, we report the purification of the catalytic (C) subunit of PKA from the posterior adductor muscle (PAM) of the sea mussel Mytilus galloprovincialis. It is a monomeric protein with an apparent molecular mass of 40.0+/-2.0kDa and Stoke's radius 25.1+/-0.3A. The protein kinase activity of the purified enzyme was inhibited by both isoforms of the PKA regulatory (R) subunit that we had previously characterized in the mollusk, and also by the inhibitor peptide PKI(5-24). On the other hand, the main proteins of the contractile apparatus of PAM were partially purified and their ability to be phosphorylated in vitro by purified PKA C subunit was analyzed. The results showed that twitchin, a high molecular mass protein associated with thick filaments, was the better substrate for endogenous PKA. It was rapidly phosphorylated with a stoichiometry of 3.47+/-0.24mol Pmol(-1) protein. Also, catchin, paramyosin, and actin were phosphorylated, although more slowly and to a lesser extent. On the contrary, myosin heavy chain (MHC) and tropomyosin were not phosphorylated under the conditions used.

Measurement of specific radioactivity in proteins separated by two-dimensional gel electrophoresis

We report a method to quantify the specific radioactivity of proteins that have been separated by 2-DE. Gels are stained with SyproRuby, and protein spots are excised. The SyproRuby dye is extracted from each spot using DMSO, and the fluorescence is quantified automatically using a plate reader. The extracted gel piece is then dissolved in hydrogen peroxide and radioactivity is quantified by liquid scintillation counting. Gentle agitation with DMSO for 24 h was found to extract all the SyproRuby dye from gel fragments. The fluorescence of the extract was linearly related to the amount of BSA loaded onto a series of 1-D gels. When rat muscle samples were run on 2-DE gels, the fluorescence extracted from 54 protein spots showed a good correlation (r = 0.79, p < 0.001) with the corresponding spot intensity measured by conventional scanning and image analysis. DMSO extraction was found not to affect the amount of radioactive protein left in the gel. When a series of BSA solutions of known specific radioactivity were run on 2-DE gels, the specific radioactivity measured by the new method showed a good correlation (r = 0.98, p < 0.01, n = 5) with the specific radioactivity measured directly before loading. Reproducibility of the method was measured in a series of 2-DE gels containing proteins from the livers of rats and mice that had been injected with [35S]methionine. Variability tended to increase when the amount of radioactivity in the protein spot was low, but for samples containing at least 10 dpm above background the CV was around 30%, which is comparable to that obtained when measuring protein expression by conventional image analysis of SyproRuby-stained 2-DE gels. Similar results were obtained whether spots were excised manually or using a spot excision robot. This method offers a high-throughput, cost-effective and reliable method of quantifying the specific radioactivity of proteins from metabolic labelling experiments carried out in vivo, so long as sufficient quantities of radioactive tracer are used.

2-DE proteome analysis of a proliferating and differentiating human neuronal stem cell line (ReNcell VM)

The proteome of a proliferating human stem cell line was analyzed and then utilized to detect stem cell differentiation-associated changes in the protein profile. The analysis was conducted with a stable human fetal midbrain stem cell line (ReNcell VM) that displays the properties of a neural stem cell. Therefore, acquisition of proteomic data should be representative of cultured human neural stem cells (hNSCs) in general. Here we present a 2-DE protein-map of this cell line with annotations of 402 spots representing 318 unique proteins identified by MS. The subsequent proteome profiling of differentiating cells of this stem cell line at days 0, 4 and 7 of differentiation revealed changes in the expression of 49 identified spots that could be annotated to 45 distinct proteins. This differentiation-associated expression pattern was validated by Western blot analysis for transgelin-2, proliferating cell nuclear antigen, as well as peroxiredoxin 1 and 4. The group of regulated proteins also included NudC, ubiquilin-1, STRAP, stress-70 protein, creatine kinase B, glial fibrillary acidic protein and vimentin. Our results reflect the large rearrangement of the proteome during the differentiation process of the stem cells to terminally differentiated neurons and offer the possibility for further characterization of specific targets driving the stem cell differentiation.

Soluble expression, purification, and stabilization of a pro-apoptotic human protein, CARP

CARP is a novel pro-apoptotic protein that has been cloned and characterized in our previous report. Previous studies showed that suppression of CARP expression results in cell proliferation in several mammalian cell lines and over-expression of CARP leads to apoptosis and inhibition of proliferation in seven tumor cell lines [Liu et al., CARP is a novel caspase recruitment domain containing pro-apoptotic protein, Biochem. Biophys. Res. Commun. 293 (2002) 1396]. To obtain soluble and active form of CARP protein for further functional and structural studies, we have expressed CARP in Escherichia coli by using Gateway cloning system. Optimal induction and expression conditions were also studied. Recombinant histidine-tagged CARP was expressed in E. coli when the carp gene was subcloned into a Gateway expression vector pET21-DEST. The partially soluble recombinant CARP protein was purified to near homogeneity by a two-step FPLC procedure, first by Ni2+ affinity chromatography followed by a gel-filtration chromatography, which yielded about 10 mg protein/L culture with at least 95% purity. Two peaks were detected in the analytical gel-filtration chromatograph while only one peak corresponding to monomer of the CARP protein was left after adding 2 mM dithiothreitol (DTT). The polymers observed are likely due to the formation of intermolecular disulfide bridges. These results suggest that adding DTT is a good solution to prevent the formation of disulfide bonds and to stabilize the protein. Successfully growing crystals of the purified CARP protein also proved that we can produce well folded CARP protein in E. coli.

Isolation and characterization of subcellular protein fractions from mouse heart

In this study, we report different protocols used to obtain highly enriched and well-characterized protein fractions that could be used to determine the subcellular localization of proteins. Different protein fractions (total, cytosolic, total membrane, sarcolemmal, and nuclear) were isolated from mouse heart by a combination of either polytron homogenization or liquid nitrogen pulverization followed by density gradient centrifugation. Triton X-100 was used in specific fractions to help in the solubilization of proteins obtained with fractionation protocols. Following the isolation, enzymatic assays and Western blot analysis were used to evaluate the enrichment and/or cross-contamination of these protein fractions. Glucose-6-phosphate dehydrogenase, Na+/K+-ATPase, mitochondrial Ca2+-ATPase, sarco-endoplasmic reticulum Ca2+-ATPase, glucose-regulated protein, and nucleoporin P62 were used as specific markers for the cytosol, sarcolemma, mitochondria, sarco-endoplasmic reticulum, endoplasmic reticulum, and nucleus, respectively. The results show that we obtained enriched protein fractions with little to no cross-contamination. These purification protocols allow us to obtain different protein fractions that could be used in a wide variety of studies.

Separation of muscle membrane from alkali-solubilized fish muscle proteins

Treatment with Ca2+ and citric acid improved membrane removal from muscle homogenates solubilized at pH 10.5 by centrifugation at 4000 g for 15 min. The percentage of phospholipid removed from muscle homogenates increased with increasing Ca2+ concentrations at 1 mM citric acid. More than 85% phospholipid and 45% protein in the muscle homogenates were removed at Ca2+ concentrations of >20 mM in the presence of 1 mM citric acid. At 8 mM Ca2+, addition of citric acid at 5 mM improved phospholipid removal to approximately 78% from 58% in its absence. Because treatment with 8 mM Ca2+ alone can remove significant amounts of phospholipid, it is likely that Ca2+ played the major role in membrane removal in muscle homogenates solubilized at pH 10.5.