Differential scanning calorimetry and circular dichroism spectrometry of walleye pollack myosin and light meromyosin

Mass spectrometry analysis and in silico prediction of allergenicity of peptides in tryptic hydrolysates of the proteins from Ruditapes philippinarum

BACKGROUND

Ruditapes philippinarum is nutrient-rich and widely-distributed, but little attention has been paid to the identification and characterization of the bioactive peptides in the bivalve. In the present study, we evaluated the peptides of the R. philippinarum that were enzymolysised by trypsin using a combination of ultra-performance liquid chromatography separation and electrospray ionization quadrupole time-of-flight tandem mass spectrometry, followed by data processing and sequence-similarity database searching. The potential allergenicity of the peptides was assessed in silico.

RESULTS

The enzymolysis was performed under the conditions: E:S 3:100 (w/w), pH 9.0, 45 °C for 4 h. After separation and detection, the Swiss-Prot database and a Ruditapes philippinarum sequence database were used: 966 unique peptides were identified by non-error tolerant database searching; 173 peptides matching 55 precursor proteins comprised highly conserved cytoskeleton proteins. The remaining 793 peptides were identified from the R. philippinarum sequence database. The results showed that 510 peptides were labeled as allergens and 31 peptides were potential allergens; 425 peptides were predicted to be nonallergenic.

CONCLUSION

The abundant peptide information contributes to further investigations of the structure and potential function of R. philippinarum. Additional in vitro studies are required to demonstrate and ensure the correct production of the hydrolysates for use in the food industry with respect to R. philippinarum. © 2017 Society of Chemical Industry.

Rapid heating of Alaska pollock and chicken breast myofibrillar protein gels as affecting water-holding properties

The gelation response of salted muscle minces to rapid versus slow heating rates is thought to differ between homeotherm and poikilotherm species. This study investigated water-holding (WH) properties of pastes prepared from refined myofibrils, at equal pH, of chicken breast versus Alaska pollock both during [cook loss (CL)] and following [expressible water (EW)] their cooking by rapid [microwave (MW)] versus slow [water bath (WB)] heating and whether such properties were related to gel matrix structure parameters and water mobility. Results did not confirm the industrial experience that pastes of meat from homeotherms benefit from slower cooking. Gels of equally high WH ability (low CL or EW) were made by rapid heating when the holding time did not exceed 5 min prior to cooling, which was sufficient for completion of gelation. Reduced CL and EW correlated with larger and smaller amplitudes of T21 and T22 water pools, respectively, measured by time-domain nuclear magnetic resonance (TD-NMR).

cDNA cloning and characterization of temperature-acclimation-associated light meromyosins from grass carp fast skeletal muscle

The three types of cDNA clones, previously defined as the 10 degrees C, intermediate and 30 degrees C-types [Tao, Y., Kobayashi, M., Liang, C.S., Okamoto, T., Watabe, S., 2004. Temperature-dependent expression patterns of grass carp fast skeletal myosin heavy chain genes. Comp. Biochem. Physiol. B 139, 649-656], were determined for their 5'-regions which encoded at least the C-terminal half of myosin rod, light meromyosin (LMM), in fast skeletal muscles of grass carp Ctenopharyngodon idella. The deduced amino acid sequence identity was 91.1% between the 10 degrees C and 30 degrees C-types and 91.4% between the 10 degrees C and intermediate-types, whereas a high sequence identity of 97.8% was found between the intermediate and 30 degrees C-types. These three grass carp LMMs all had a characteristic seven-residue (heptad) repeat (a, b, c, d, e, f, g)(n), where positions a and d were normally occupied by hydrophobic residues, and positions b, c and f by charged residues. However, the ratios of hydrophobic residues to the total were higher for the intermediate- and 30 degrees C- than 10 degrees C-type LMM, suggesting that the former both types may form more stable coiled-coils of alpha-helices than the latter type. These differences in the primary structures of LMM isoforms might be partially implicated in differences in the thermostabilities and gel-forming profiles of myosins from grass carp in different seasons reported previously [Tao, Y., Kobayashi, M., Fukushima, H., Watabe, S., 2005. Changes in enzymatic and structural properties of grass carp fast skeletal myosin induced by the laboratory-conditioned thermal acclimation and seasonal acclimatization. Fish. Sci. 71, 195-204; Tao, Y., Kobayashi, M., Fukushima, H., Watabe, S., 2007. Changes in rheological properties of grass carp fast skeletal myosin induced by seasonal acclimatization. Fish. Sci. 73, 189-196].

Conformational and rheological changes in catfish myosin as affected by different acids during acid-induced unfolding and refolding

Changes in the conformation of catfish (Ictalurus punctatus) myosin due to (i) anions, (ii) acid pH, and (iii) salt addition were determined using tryptophan fluorescence, hydrophobicity measurements, differential scanning calorimetry, and circular dichroism. The relationship between conformation and storage modulus (G') of acid-treated myosin was studied. Three acids, HCl, H2SO4, and H3PO4, were used for unfolding myosin at three acidic pH conditions, 1.5, 2.0, and 2.5. Unfolded myosin was refolded to pH 7.3. Denaturation and unfolding of myosin was significantly (p < 0.05) lower when salt (0.6 M NaCl) was present during acid unfolding than in the absence of salt. When salt was added before unfolding, the alpha-helix content of myosin treated at pH 1.5 was significantly lower than that treated at pH 2.5. When salt was added after refolding, the alpha-helix content of myosin was unaffected by different pH treatments. The G' of myosin increased with an increase in myosin denaturation. The G' of myosin was significantly (p < 0.05) higher when salt was added to myosin after refolding than before acid unfolding. Among the different anion treatments, the G' of acid-treated myosin decreased in the order Cl- approximately SO42- > PO43-. Among the different pH treatments, the G' of myosin treated at pH 1.5 was significantly (p < 0.05) higher than myosin treated at pH 2.5. The conditions that would result in maximum myosin denaturation and maximum G' were unfolding of myosin at pH 1.5 using Cl- (from HCl) followed by refolding at pH 7.3 and subsequent addition of 0.6 M NaCl.

Relationship between seawater pollution and qualitative changes in the extracted proteins from mussels Mytilus galloprovincialis

The aim of this study was to find a reliable biomarker of seawater pollution. For this purpose the contents of Zn and Cu, proteins and antioxidant activity in mussels Mytilus galloprovincialis collected from polluted and non-polluted sites of the Bulgarian Black Sea coast were compared. To determine the above-mentioned indices atomic spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, fluorescence, differential scanning calorimetry (DSC), and two antioxidant tests were used. It was found that the amounts of Zn and Cu were significantly higher in the mussel proteins from the polluted than from the non-polluted sites (P<0.05). FT-IR spectroscopy and fluorescence revealed specific qualitative changes in secondary and tertiary structures in mussel proteins in the samples from polluted sites. The thermodynamic properties of proteins and the changes upon denaturation were correlated with the secondary structure of proteins and disappearance of alpha-helix. Purified protein scavenging activity against 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(*+)) was significantly higher in mussel samples from polluted than from non-polluted sites. Therefore, the changes in Zn and Cu concentration, in protein's secondary and tertiary structures and antioxidant activity in mussels M. galloprovincialis from polluted sites can be a reliable biomarker of the level of the seawater pollution.

Rheological properties of fast skeletal myosin rod and light meromyosin from walleye pollack and white croaker: contribution of myosin fragments to thermal gel formation

Myosin rod and light meromyosin (LMM) of walleye pollack and white croaker were examined for their rheological properties by measuring dynamic viscoelastic parameters. Rods from walleye pollack and white croaker increased their storage moduli (G') in the ranges of 29-43 degrees C and 31-38 degrees C, respectively, in temperature sweep analysis. Walleye pollack LMM showed no peak of G' upon heating, whereas the white croaker counterpart exhibited a single sharp peak of G' at 35 degrees C. Loss modulus (G") showed similar temperature-dependent changes for the two fish species as the case of G', irrespective of rod and LMM, although G" values were lower than those of G'. Thus, rheological properties of rod and LMM were different between walleye pollack and white croaker. Taken together with data previously reported for myosin, it was considered that both myosin rods from walleye pollack and white croaker are attributed to thermal gel formation of myosin in a low-temperature range, though in a species-specific manner.

Differences in polymer formation through disulfide bonding of recombinant light meromyosin between white croaker and walleye pollack and their possible relation to species specific differences in thermal unfolding

Fast skeletal light meromyosins (LMMs) of white croaker and walleye pollack were prepared in our expression system using Escherichia coli and determined for their polymer-forming ability and thermodynamic properties by using sodium dodecyl sulfate polyacrylamide gel electrophoresis and differential scanning calorimetry (DSC), respectively. White croaker LMM formed dimer by heating at 80 degrees C and showed only a single peak at 32.1 degrees C of temperature transition in DSC. On the other hand, walleye pollack LMM hardly formed polymer and showed four peaks at 27.7, 30.5, 35.8, and 43.9 degrees C. When Cys525 of white croaker LMM was replaced by alanine, this point-mutated LMM showed no change in its DSC profile but formed no dimer upon heating, suggesting a possible role of Cys525 in dimer formation. On the other hand, walleye pollack LMM where Cys491 was substituted by alanine changed its DSC profile, showing four peaks at 27.9, 29.1, 38.4, and 43.9 degrees C. However, this point-mutated LMM formed no dimer upon heating as in the case of native LMM. These results suggest that cysteine residue(s) participates in thermal gel formation of LMM when it locates in a suitable position of the sequence.