Purification and characterization of pepsinogens and pepsins from the stomach of rice field eel (Monopterus albus Zuiew)

Biochemical characterization of acid proteases from the stomach of palometa (Pygocentrus nattereri, Kner 1858) with potential industrial application

Pepsin is one of the major enzymes with significant importance in the food industry, biomedicines, and pharmaceutical formulations. In this work, the main objective was to biochemically characterize a pepsin-like enzymatic extract obtained from Pygocentrus nattereri, a predatory freshwater fish, focusing on their potential industrial application. The obtained extract exhibited optimal activity at 45 °C and pH 1.0-2.0. These proteases remained stable after 2 h of incubation at temperatures ranging from 0° to 45 °C and within pH range of 1.0 to 7.0. Their activity was significantly affected in presence of pepstatin A and SDS, 10 μM and 3.46 mM respectively, while EDTA and PMSF showed partial inhibitory effects. Divalent cations (Ca2+ and Mg2+) did not inhibit the proteolytic activity of the extract; in fact, it improved at a 5 mM CaCl2 concentration. As the NaCl concentration increased, the enzyme activity decreased. However, after desalination, 90 % of the activity was recovered within the tested exposure time. Besides, this extract demonstrated exceptional versatility across diverse industrial applications, including collagen extraction augmentation, IgG hydrolysis facilitation, and silver and polyester recovery from X-ray films. Our results suggest that the obtained enzymatic extract has a wide range of potential applications.

Enzymological characteristics of pepsinogens and pepsins purified from lizardfish (Saurida micropectoralis) stomach

One major pepsinogen, PG-I, and two minor pepsinogens, PG-II and PG-III were purified from lizardfish stomach by ammonium sulfate precipitation and two chromatographic columns. The three purified PGs migrated as single bands in native-PAGE gels with molecular weights (MW) ranging from 36 to 38 kDa. Each PG was converted to pepsin (P) at pH 2.0, and the MW were determined as 32 kDa (for P-I), 31 kDa (for P-II) and 30 kDa (for P-III). The optimum pH and temperature of pepsins were 2.0-3.5, and 40-50 °C. All 3 pepsins were strongly inhibited by pepstatin A. Divalent cations slightly stimulated the pepsin activities, but ATP had no effect on the pepsins. Purified pepsins were effective in the hydrolysis of various proteins. K_m and k_cat of the three pepsins for hemoglobin hydrolysis were 107.64-276.61 µM and 18.30-32.68 s^-1, respectively. The new pepsins have potential for use in protein food procession and modification.

Pathogenicity of snakehead vesiculovirus in rice field eels (Monopterus albus)

Snakehead vesiculovirus (SHVV) has caused mass mortality to cultured snakehead fish in China, resulting in enormous economic losses in snakehead fish culture. In this report, the whole genome of SHVV was sequenced. Interestingly, it shared more than 94% nucleotide sequence identity with Monopterus albus rhabdovirus (MoARV), which has caused great economic loss to cultured rice field eel (Monopterus albus). Therefore, the concern of cross-species infection of these viruses prompted us to investigate the susceptibility of rice field eel to SHVV infection. The results showed that rice field eel was susceptible to SHVV in both intracoelomical injection and immersion routes. Severe hemorrhage was observed on the skin and visceral organs of SHVV-infected rice field eels. Histopathological examination showed vacuoles in the tissues of infected liver, kidney and heart. Viral RNA or protein was detected in the tissues of infected fish by reverse transcription polymerization chain reaction (RT-PCR), in situ hybridization (ISH), or immunohistochemistry assay (IHC). Investigation of the epidemic of vesiculovirus in rice field eel as well as other co-cultured fish is invaluable for the prevention of vesiculovirus infection.

Pepsinogens and pepsins from largemouth bass, Micropterus salmoides: purification and characterization with special reference to high proteolytic activities of bass enzymes

Six pepsinogens were purified from the gastric mucosa of largemouth bass (Micropterus salmoides) by DEAE-Sephacel chromatography, Sephadex G-100 gel filtration, and Mono Q FPLC. The potential specific activities of two major pepsinogens, PG1-1 and PG2-2, against hemoglobin were 51 and 118 units/mg protein, respectively. The activity of pepsin 2-2 was the highest among the pepsins reported to date; this might be linked to the strongly carnivorous diet of the largemouth bass. The molecular masses of PG1-1 and PG2-2 were 39.0 and 41.0 kDa, respectively. The N-terminal amino acid sequences of PG1-1 and PG2-2 were LVQVPLEVGQTAREYLE- and LVRLPLIVGKTARQALLE-, respectively, showing similarities with those of fish type-A pepsinogens. The optimal pHs for hemoglobin-digestive activity of pepsins 1-1 and 2-2 were around 1.5 and 2.0, respectively, though both pepsins retained considerable activity at pHs over 3.5. They showed maximal activity around 50 and 40 °C, respectively. They were inhibited by pepstatin similarly to porcine pepsin A. The cleavage specificities clarified with oxidized insulin B chain were shown to be restricted to a few bonds consisting of hydrophobic/aromatic residues, such as the Leu(15)-Tyr(16), Phe(24)-Phe(25) and Phe(25)-Tyr(26) bonds. When hemoglobin was used as a substrate, the kcat/Km value of bass pepsin 2-2 was 4.6- to 36.8-fold larger than those of other fish pepsins. In the case of substance P, an ideal pepsin substrate mimic, the kcat/Km values were about 200-fold larger than those of porcine pepsin A, supporting the high activity of the bass pepsin.

Isolation and identification of a lethal rhabdovirus from farmed rice field eels Monopterus albus

We provide the first description of a virus responsible for a systemic hemorrhagic disease causing high mortality in farmed rice field eels Monopterus albus in China. Typical signs exhibited by the diseased fish were extensive hemorrhages in the skin and viscera and some neurological signs, such as loss of equilibrium and disorganized swimming. Histopathological examination revealed various degrees of necrosis within the spleen and liver. Virus isolation was attempted from visceral tissues of diseased fish by inoculation on 6 fish cell lines. Typical cytopathic effects (CPE) were produced in bluegill fry (BF2) cells, so this cell line was chosen for further isolation and propagation of the virus. Electron microscopy observation showed that the negative stained viral particles had the characteristic bullet shape of rhabdoviruses and an estimated size of 60 × 120 nm. We therefore tentatively refer to this virus as Monopterus albus rhabdovirus (MoARV). Molecular characterization of MoARV, including sequence analysis of the nucleoprotein (N), phosphoprotein (P), and glycoprotein (G) genes, revealed 94.5 to 97.3% amino acid similarity to that of Siniperca chuatsi rhabdovirus. Phylogenetic analysis based on the amino acid sequences of N and G proteins indicated that MoARV should be a member of the genus Vesiculovirus. Koch's postulates were fulfilled by infecting healthy rice field eels with MoARV, which produced an acute infection. RT-PCR analysis demonstrated that MoARV RNA could be detected in both naturally and experimentally infected fish. The data suggest that MoARV was the causative pathogen of the disease.

Accessing the reproducibility and specificity of pepsin and other aspartic proteases

The aspartic protease pepsin is less specific than other endoproteinases. Because aspartic proteases like pepsin are active at low pH, they are utilized in hydrogen deuterium exchange mass spectrometry (HDX MS) experiments for digestion under hydrogen exchange quench conditions. We investigated the reproducibility, both qualitatively and quantitatively, of online and offline pepsin digestion to understand the compliment of reproducible pepsin fragments that can be expected during a typical pepsin digestion. The collection of reproducible peptides was identified from >30 replicate digestions of the same protein and it was found that the number of reproducible peptides produced during pepsin digestion becomes constant above 5-6 replicate digestions. We also investigated a new aspartic protease from the stomach of the rice field eel (Monopterus albus Zuiew) and compared digestion efficiency and specificity to porcine pepsin and aspergillopepsin. Unique cleavage specificity was found for rice field eel pepsin at arginine, asparagine, and glycine. Different peptides produced by the various proteases can enhance protein sequence coverage and improve the spatial resolution of HDX MS data. This article is part of a Special Issue entitled: Mass spectrometry in structural biology.