Elena Shumilina

NMR approach for monitoring post-mortem changes in Atlantic salmon fillets stored at 0 and 4°C.

High resolution NMR technique has been used to monitor post-mortem changes in salmon (Salmo salar) fillets upon storage at 4 and 0°C. Thirty-one different fish metabolites influencing freshness and taste properties have been unequivocally assigned by NMR using either available standard compounds or ad hoc acquired 2D (1)H-(1)H TOCSY and (1)H-(13)С HSQC spectra. The monitored fish metabolites include amino acids, dipeptides, sugars, vitamins, biogenic amines, as well as different products of the ATP degradation. The detection and monitoring of biogenic amines by NMR, upon fish storage, is information of interest for consumers, since some of these compounds are toxic. The data from this study shows that NMR spectroscopy also provides the amount of all metabolites necessary for the calculation of the K-index used to express fish freshness. A good correlation was found between the K-index increase and the formation of the undesired biogenic amines. The metabolite concentrations and the K-index found in this work were compared and found coherent with literature data. The performed study reveals the strengths and the suitability of the NMR approach to monitor different biochemical processes occurring during fish storage and qualitatively and quantitatively characterise fish metabolites determining fish quality.

Quality changes of salmon by-products during storage: Assessment and quantification by NMR

Safe utilization of fish by-products is an important task due to increasing fish consumption. It can provide new valuable food/feed and will increase the economical profit and sustainability of the fishery industry. NMR spectroscopy is a reliable tool able to monitor qualitative and quantitative changes in by-products. In this work the trichloroacetic acid extracts of salmon backbones, heads and viscera stored at industrially relevant temperatures (4 and 10°C) were studied using NMR. Twenty-five metabolites were detected and the possibility of salmon by-products utilization as a source of anserine, phosphocreatine and taurine was discussed. Statistical data elaboration allowed determining the main processes occurring during by-products storage: formation of trimethylamine and biogenic amines, proteolysis and different types of fermentations. By-products freshness was evaluated using a multi-parameter approach: the trimethylamine and biogenic amines concentration changes were compared with Ki and H-values and safe temperatures and times for storage of salmon by-products were proposed.

Structural Analysis of Glutaredoxin Domain of Mus musculus Thioredoxin Glutathione Reductase

Thioredoxin glutathione reductase (TGR) is a member of the mammalian thioredoxin reductase family that has a monothiol glutaredoxin (Grx) domain attached to the thioredoxin reductase module. Here, we report a structure of the Grx domain of mouse TGR, determined through high resolution NMR spectroscopy to the final backbone RMSD value of 0.48±0.10 Å. The structure represents a sandwich-like molecule composed of a four stranded β-sheet flanked by five α–helixes, with the CxxS active motif located on the catalytic loop. We structurally characterized the glutathione-binding site in the protein and describe sequence and structural relationships of the domain with glutaredoxins. The structure illuminates a key functional center that evolved in mammalian TGRs to act in thiol-disulfide reactions. Our study allows us to hypothesize that Cys105 might be functionally relevant for TGR catalysis. In addition, the data suggest that the N-terminus of Grx acts as a possible regulatory signal also protecting the protein active site from unwanted interactions in cellular cytosol.

Structural Insights into Interaction between Mammalian Methionine Sulfoxide Reductase B1 and Thioredoxin

Maintenance of the cellular redox balance has vital importance for correcting organism functioning. Methionine sulfoxide reductases (Msrs) are among the key members of the cellular antioxidant defence system. To work properly, methionine sulfoxide reductases need to be reduced by their biological partner, thioredoxin (Trx). This process, according to the available kinetic data, represents the slowest step in the Msrs catalytic cycle. In the present paper, we investigated structural aspects of the intermolecular complex formation between mammalian MsrB1 and Trx. NMR spectroscopy and biocomputing were the two mostly used through the research approaches. The formation of NMR detectable MsrB1/Trx complex was monitored and studied in attempt to understand MsrB1 reduction mechanism. Using NMR data, molecular mechanics, protein docking, and molecular dynamics simulations, it was found that intermediate MsrB1/Trx complex is stabilized by interprotein β-layer. The complex formation accompanied by distortion of disulfide bond within MsrB1 facilitates the reduction of oxidized MsrB1 as it is evidenced by the obtained data.

Development of a statistical model to detect quality and storage conditions of Atlantic salmon

The ever-increasing demand for fish as a food, has led to the development of new handling and packaging technologies resulting in premium quality fish products. In order to avoid frauds reaching the market, fish quality assurance methods need to be developed. In this study, two statistical models of biochemical processes that occur in Atlantic salmon during two weeks of storage at 0 and 4 °C were developed. These models were further used to detect salmon quality and its storage conditions. The biochemical processes were monitored using Nuclear Magnetic Resonance (NMR) spectroscopy and principal component analysis (PCA). The Soft Independent Modeling of Class Analogy (SIMCA) approach was applied to develop and evaluate the models. The fraud detection potential of the models was tested using samples of various quality and storage parameters. It was shown that the developed models are able to discriminate quality, time and temperature of stored Atlantic salmon.

Evaluation of the potential of utilizing lactic acid bacteria and dairy wastewaters for methane production

The aim of this study was to assess the potential of utilizing Lactobacillus delbrüeckii spp. bulgaricus in order to improve the characteristics of dairy wastewater and produce biomethane. Nuclear magnetic resonance was utilized to assess the metabolites present in the unprocessed wastewater. It was determined that wastewater is a good source of important bio-refinery relevant compounds and therefore wastewater has a potential to be utilized during fermentation as nutrients source. Upon wastewater fermentation, the chemical oxygen demand and biological oxygen demand significantly decreased (respectively 97.0 and 97.8%). Protocols were tested for one- and two-stage fermentation. During the one-stage fermentation, lactic acid bacteria were not added to the wastewater. During the two-stage fermentation, acetogenesis and methanogenesis occurred separately with the addition of L. delbdueckii during the acetogenesis stage. The highest yield of methane was obtained from wastewater upon two-stage fermentation (76% two-stages compared to 38% one-stage). Therefore, L. delbrüeckii have the potential to be utilized to ferment dairy WWs and produce methane. Such treatment of wastewater not only produces methane, but also decreases the polluting effect of the waste streams, by reducing the chemical oxygen demand and biological oxygen demand to 0.199 and 0.031 g/l, respectively.

Potential of an Exploitation of Acid-Tolerant Antimicrobial Microorganisms Evolving Enzyme Systems for the Utilization of Dairy By-products and Lignocellulosic Biomass to Lactic Acid.

Citation: Juodeikiene G, Zadeike D, Bartkiene E, Bartkevics V, Dikiy A and Shumilina E (2016) Potential of an Exploitation of AcidTolerant Antimicrobial Microorganisms Evolving Enzyme Systems for the Utilization of Dairy By-products and Lignocellulosic Biomass to Lactic Acid. Front. Bioeng. Biotechnol. 4:92. doi: 10.3389/fbioe.2016.00092 potential of an Exploitation of Acid-Tolerant Antimicrobial Microorganisms Evolving Enzyme Systems for the Utilization of Dairy By-products and Lignocellulosic Biomass to Lactic Acid

1H, 13C, and 15N NMR resonance assignments of reduced full length and shortened forms of the Grx domain of Mus musculus TGR

Two forms of the glutaredoxin (Grx) domain (full length Grx domain and short Grx lacking the N-terminal region) of Mus musculus thioredoxin glutathione reductase (TGR) were isotopically labelled with 15N and 13C isotopes, expressed and purified to homogeneity. We report here the 1H, 13C and 15N NMR assignment for both Grx forms of this mouse TGR. This investigation represents the first NMR analysis of a mammalian TGR.

Evolution of Structural and Coordination Features Within the Methionine Sulfoxide Reductase B Family

In this review, we summarize the evolution, sequence, structural and coordination peculiarities of proteins belonging to the Methionine Sulfoxide Reductase B family (MsrBs). These proteins represent important redox proteins. MsrBs are found in all kingdoms of life. Whereas prokaryotes have only one type of MsrB, mammals possess three, MsrB1, MsrB2 and MsrB3, distributed in different cellular compartments, and regulated by alternative splicing and specific targeting signals. Structural analysis of mammalian and bacterial MsrBs revealed a well-conserved β-core, and dramatic variability in C-and N-terminus. Mostly, MsrBs contain structural zinc ions coordinated by four cysteines. However, some of MsrBs lack coordinating cysteines and, therefore may not contain zinc ion.