Fish muscle parvalbumins as marker proteins for native and urea isoelectric focusing

Parvalbumin: A Major Fish Allergen and a Forensically Relevant Marker

Parvalbumins (PVALBs) are low molecular weight calcium-binding proteins. In addition to their role in many biological processes, PVALBs play an important role in regulating Ca2+ switching in muscles with fast-twitch fibres in addition to their role in many biological processes. The PVALB gene family is divided into two gene types, alpha (α) and beta (β), with the β gene further divided into two gene types, beta1 (β1) and beta2 (β2), carrying traces of whole genome duplication. A large variety of commonly consumed fish species contain PVALB proteins which are known to cause fish allergies. More than 95% of all fish-induced food allergies are caused by PVALB proteins. The authentication of fish species has become increasingly important as the seafood industry continues to grow and the growth brings with it many cases of food fraud. Since the PVALB gene plays an important role in the initiation of allergic reactions, it has been used for decades to develop alternate assays for fish identification. A brief review of the significance of the fish PVALB genes is presented in this article, which covers evolutionary diversity, allergic properties, and potential use as a forensic marker.

Proteomics for the authentication of fish species

Assessment of seafood authenticity and origin, mainly in the case of processed products (fillets, sticks, baby food) represents the crucial point to prevent fraudulent deceptions thus guaranteeing market transparency and consumers health. The most dangerous practice that jeopardies fish safety is intentional or unintentional mislabeling, originating from the substitution of valuable fish species with inferior ones. Conventional analytical methods for fish authentication are becoming inadequate to comply with the strict regulations issued by the European Union and with the increase of mislabeling due to the introduction on the market of new fish species and market globalization. This evidence prompts the development of high-throughput approaches suitable to identify unambiguous biomarkers of authenticity and screen a large number of samples with minimal time consumption. Proteomics provides suitable and powerful tools to investigate main aspects of food quality and safety and has given an important contribution in the field of biomarkers discovery applied to food authentication. This report describes the most relevant methods developed to assess fish identity and offers a perspective on their potential in the evaluation of fish quality and safety thus depicting the key role of proteomics in the authentication of fish species and processed products.

BIOLOGICAL SIGNIFICANCE

The assessment of fishery products authenticity is a main issue in the control quality process as deceptive practices could imply severe health risks. Proteomics based methods could significantly contribute to detect falsification and frauds, thus becoming a reliable operative first-line testing resource in food authentication.

Proteomics in food: Quality, safety, microbes, and allergens

Food safety and quality and their associated risks pose a major concern worldwide regarding not only the relative economical losses but also the potential danger to consumer's health. Customer's confidence in the integrity of the food supply could be hampered by inappropriate food safety measures. A lack of measures and reliable assays to evaluate and maintain a good control of food characteristics may affect the food industry economy and shatter consumer confidence. It is imperative to create and to establish fast and reliable analytical methods that allow a good and rapid analysis of food products during the whole food chain. Proteomics can represent a powerful tool to address this issue, due to its proven excellent quantitative and qualitative drawbacks in protein analysis. This review illustrates the applications of proteomics in the past few years in food science focusing on food of animal origin with some brief hints on other types. Aim of this review is to highlight the importance of this science as a valuable tool to assess food quality and safety. Emphasis is also posed in food processing, allergies, and possible contaminants like bacteria, fungi, and other pathogens.

Differentiation between fresh and frozen-thawed sea bass (Dicentrarchus labrax) fillets using two-dimensional gel electrophoresis

This study aimed to identify a protein marker that can differentiate between fresh skinless and frozen-thawed sea bass (Dicentrarchus labrax) fillets using the two-dimensional polyacrylamide gel electrophoresis (2-DE) technique. Distinct gel patterns, due to proteins with low molecular weight and low isoelectric points, distinguished fresh fillets from frozen-thawed ones. Frozen-thawed fillets showed two specific protein spots as early as the first day of the study. However, these spots were not observed in fresh fillets until at least 13days of storage between 0 and 4°C, fillets were judged, beyond this period, fish were unfit for human consumption as revealed by complementary studies on fish spoilage indicators namely total volatile basic nitrogen and biogenic amines. Mass spectrometry identified the specific proteins as parvalbumin isoforms. Parvalbumins may thus be useful markers of differentiation between fresh and frozen-thawed sea bass fillets.

A Ca(2+)-binding protein with numerous roles and uses: parvalbumin in molecular biology and physiology

Parvalbumins (PVs) are acidic, intracellular Ca(2+)-binding proteins of low molecular weight. They are associated with several Ca(2+)-mediated cellular activities and physiological processes. It has been suggested that PV might function as a "Ca2+ shuttle" transporting Ca2+ from troponin-C (TnC) to the sarcoplasmic reticulum (SR) Ca2+ pump during muscle relaxation. Thus, PV may contribute to the performance of rapid, phasic movements by accelerating the contraction-relaxation cycle of fast-twitch muscle fibers. Interestingly, PVs promote the generation of power stroke in fish by speeding up the rate of relaxation and thus provide impetus to attain maximal sustainable speeds. However, immunological monitoring of diverse tissues demonstrated that PVs are also present in non-muscle cells. The axoplasmic transport and various intracellular secretory mechanisms including the endocrine secretions seem to be controlled by the Ca2+ regulation machinery. Any defect in the Ca2+ handling apparatus may cause several clinical problems; for instance, PV deficiency alters the neuronal activity, a key mechanism leading to epileptic seizures. Moreover, atypical relaxation of the heart results in diastolic dysfunction, which is a major cause of heart failure predominantly among the aged people. PV may offer a unique potential to correct defective relaxation in energetically compromised failing hearts through PV gene transfer. Consequently, PV gene transfer may present a new therapeutic approach to correct cellular disturbances in Ca2+ signaling pathways of diseased organs. Hence, PVs appear to be amazingly useful candidate proteins regulating a variety of cellular functions through action on Ca2+ flux management.

Fish authentication by MALDI-TOF mass spectrometry

Recent EU directives and regulations for quality control and authentication of food products have prompted the development of new methods for large-scale tests to ensure the protection of consumers. In view of this, an innovative method based on MALDI-TOF mass spectrometry has been developed and successfully applied to fish authentication. Highly specific mass spectrometric profiles from 25 different fish species were obtained. Signals generated from proteins with molecular weights of about 11 kDa have been selected as specific biomarkers for unambiguous discrimination. This method is also suitable for verifying commercial product authenticity and to rapidly discriminate species subjected to fraudulent substitutions, such as those belonging to Gadidae and Pleuronectiformes. For example, biomarkers for fillets of sole (m/z 11975.21), European plaice (m/z 11351.73, 11763.63) and Greenland halibut (m/z 11432.38) were defined. Structural characterization by mass spectrometry of several proteins generating biomarker signals allowed us to identify them as parvalbumins, known to be among the major fish allergens.

Identification of commercial hake and grenadier species by proteomic analysis of the parvalbumin fraction

Analysis of parvalbumin fractions through proteomic methodologies allowed the differential classification of ten commercial, closely related species of the family Merlucciidae. Muscle extracts from nine hake species of the genus Merluccius including two subspecies of Merluccius australis (australis and polylepsis) and one grenadier species Macruronus novaezelandiae with two populations (novaezelandiae and magellanicus) were evaluated by 2-DE and MALDI-TOF MS. 2-DE demonstrated that the species tested displayed a low intra-specific degree of polymorphism and the isoform patterns were noticeably species-specific. MALDI-TOF mass fingerprints showed clear differences in the pattern of peptides produced by tryptic digestion between the Merluccius and the Macruronus, making the genus differentiation possible. In addition, a selective peptide mass present in the spectra from certain hakes allowed its classification in two groups: Euro-African and American hakes. Besides, some specific masses allowed a clearly individual identification for M. bilinearis, M. australis polylepsis, M. australis australis, M. productus, M. paradoxus and M. polli, while the rest of the hake species can be grouped in two clusters, comprising M. hubbsi and M. gayi in one and M. merluccius and M. capensis in the other.

Preliminary study on puffer fish proteome-species identification of puffer fish by two-dimensional electrophoresis

The aims of this work were to determine the differential characterization of the urea soluble protein components of puffer fish species and to establish a preliminary proteomic database using an immobilized pH gradient two-dimensional electrophoresis (2DE) technique. The puffer fish muscle proteins resolved into 171-260 spots in the 2DE gels, with a pI range of 3-10 and molecular mass range of 7.4-205.0 kDa, following Comassie blue staining. Puffer fish muscle proteins fell in the region with pI values of 3.5-7.0, and molecular masses of 7.4-45.0 kDa were well-resolved and were good for species comparison. The more acidic proteins of lower molecular masses showed species specific characteristics. Therefore, the species of puffer fish can be differentiated from the comparison of the characteristic 2DE protein patterns.

Computer-assisted evaluation of isoelectric focusing patterns in electrophoretic gels: identification of smoothhounds (Mustelus mustelus, Mustelus asterias) and comparison with lower value shark species

In this work, the most commercially important Selachian species, smoothhound (Mustelus mustelus) and starry smoothhound (Mustelus asterias), have been identified by polyacrylamide isoelectric focusing (IEF-PAGE), along with several shark species of minor commercial value. In Italy, these two smoothhound species are commonly subjected to fraudulent substitution with lesser valued sharks. After the electrophoretic runs, the band patterns of the two Mustelus species were compared with those of dogfish (Scyliorhinus canicula), spurdog (Squalus acanthias), blue shark (Prionace glauca) and black-mouthed dogfish (Galeus melanostomus), both visually and with gel analysis software. The actual isoelectric points were then submitted to cluster analysis to differentiate the single species, despite the possible occurrence of electrophoretic variations or protein polymorphism. Every shark showed species-specific band patterns and could therefore be well differentiated, as confirmed by statistical analysis.