Histamine dehydrogenase from Rhizobium sp.: gene cloning, expression in Escherichia coli, characterization and application to histamine determination

Structure of Rhizobium sp. 4-9 histamine dehydrogenase and analysis of the electron transfer pathway to an abiological electron acceptor

Histamine dehydrogenase from the gram-negative bacterium Rhizobium sp. 4-9 (HaDHR) is a member of a small family of dehydrogenases containing a covalently attached FMN, and the only member so far identified to date that does not exhibit substrate inhibition. In this study, we present the 2.1 Å resolution crystal structure of HaDHR. This new structure allowed for the identification of the internal electron transfer pathway to abiological ferrocene-based mediators. Alanine 437 was identified as the exit point of electrons from the Fe₄S₄ cluster. The enzyme was modified with a Ser436Cys mutation to facilitate covalent attachment of a ferrocene moiety. When modified with Fc-maleimide, this new construct demonstrated direct electron transfer from the enzyme to a gold electrode in a histamine concentration-dependent manner without the need for any additional electron mediators.

Modulating Substrate Specificity of Rhizobium sp. Histamine Dehydrogenase through Protein Engineering for Food Quality Applications

Histamine is a biogenic amine found in fish-derived and fermented food products with physiological relevance since its concentration is proportional to food spoilage and health risk for sensitive consumers. There are various analytical methods for histamine quantification from food samples; however, a simple and quick enzymatic detection and quantification method is highly desirable. Histamine dehydrogenase (HDH) is a candidate for enzymatic histamine detection; however, other biogenic amines can change its activity or produce false positive results with an observed substrate inhibition at higher concentrations. In this work, we studied the effect of site saturation mutagenesis in Rhizobium sp. Histamine Dehydrogenase (Rsp HDH) in nine amino acid positions selected through structural alignment analysis, substrate docking, and proximity to the proposed histamine-binding site. The resulting libraries were screened for histamine and agmatine activity. Variants from two libraries (positions 72 and 110) showed improved histamine/agmatine activity ratio, decreased substrate inhibition, and maintained thermal resistance. In addition, activity characterization of the identified Phe72Thr and Asn110Val HDH variants showed a clear substrate inhibition curve for histamine and modified kinetic parameters. The observed maximum velocity (V_max) increased for variant Phe72Thr at the cost of an increased value for the Michaelis-Menten constant (K_m) for histamine. The increased K_m value, decreased substrate inhibition, and biogenic amine interference observed for variant Phe72Thr support a tradeoff between substrate affinity and substrate inhibition in the catalytic mechanism of HDHs. Considering this tradeoff for future enzyme engineering of HDH could lead to breakthroughs in performance increases and understanding of this enzyme class.

Histamine-degrading halophilic bacteria from traditional fish sauce: Characterization of Virgibacillus campisalis TT8.5 for histamine reduction

Traditionally produced fish sauce can contain significant amounts of histamine. In some instances, the histamine concentration may be well above the limit recommended by the Codex Alimentarius Commission. The aim of this study was to discover new bacterial strains capable of growing under the stressful environmental conditions of fish sauce fermentation and metabolizing histamine. In this study, 28 bacterial strains were isolated from Vietnamese fish sauce products based on their ability to grow at high salt concentrations (23% NaCl) and tested for their ability to degrade histamine. Strain TT8.5 showed the highest histamine-degradation (45.1 ± 0.2% of initially 5 mM histamine within 7 days) and was identified as Virgibacillus campisalis TT8.5. Its histamine-degrading activity was shown to be localized intracellularly and the enzyme is a putative histamine dehydrogenase. The strain exhibited optimal growth and histamine-degrading activity at 37°C, pH 7%, and 5% NaCl in halophilic archaea (HA) histamine broth. It also showed pronounced histamine-degrading activity in HA histamine broth when cultivated at temperatures of up to 40 °C as well as in the presence of up to 23% NaCl. After treatment with immobilized cells, 17.6-26.9% of the initial histamine in various fish sauce products were reduced within 24 h of incubation, while no significant changes in other parameters of fish sauce quality were observed after this treatment. Our results indicate that V. campisalis TT8.5 is of potential interest to be applied in histamine degradation of traditional fish sauce.

Histamine and Scombrotoxins

Histamine intoxications result when histamine-metabolizing enzymes are compromised or overwhelmed by dietary histamine in the human body. This can occur either due to metabolic enzyme deficiencies, such as in histamine intolerance to wines, aged cheese and other foods or from high concentrations of histamine following ingestion of decomposed fish. The presence of histamine in decomposed fish and fish products results from bacterial decarboxylation of free L-histidine following product mishandling. Consequently, histamine intoxications from mishandled fish, commonly referred to as scombrotoxin fish poisoning (SFP) or scombroid poisoning, require high levels of free L-histidine only found in certain species of pelagic fish. Differential diagnosis is required of clinicians since dietary histamine intoxications produce the same symptoms typical of release of endogenous histamine due to IgE -mediated seafood allergies or anisakiasis. Although high levels of dietary histamine are responsible for SFP, histamine has important physiological functions and tends to exert toxic effects only at doses beyond the physiological range. Endogenous histamine is essential to local immune responses, regulation of gastric acid secretion in the gut, and neurotransmission in the central nervous system. Scombrotoxins, postulated to explain histamine's augmented toxicity in scombrotoxic fish, are a milieu of histamine and other bioactives. Since time-and-temperature abuse is required to produce high levels of histamine in fish, management consists of ensuring proper handling by identifying hazards and critical control points (HACCP) and maintaining a "cold chain" from catch to consumption. Reference methods for detecting histamine have received increased attention and the European Commission has validated a popular precolumn dansylation-based HPLC method through inter-laboratory collaboration and studied method equivalence with the AOAC fluorescence method 977.13 recognized by Codex Alimentarius. Much progress has been made during the last decade in the development and validation of rapid screening methods for detecting histamine in food and especially in fish products. These include many innovative sensors and several validated commercial test kits, many of them based on a recombinant form of the enzyme histamine dehydrogenase (HD).

Structural insights into the enhanced thermostability of cysteine substitution mutants of L-histidine decarboxylase from Photobacterium phosphoreum

Enzymatic amino acid assays are important in physiological research and clinical diagnostics because abnormal amino acid concentrations in biofluids are associated with various diseases. L-histidine decarboxylase from Photobacterium phosphoreum (PpHDC) is a pyridoxal 5'-phosphate-dependent enzyme and a candidate for use in an L-histidine quantitation assay. Previous cysteine substitution experiments demonstrated that the PpHDC C57S mutant displayed improved long-term storage stability and thermostability when compared with those of the wild-type enzyme. In this study, combinational mutation experiments of single cysteine substitution mutants of PpHDC were performed, revealing that the PpHDC C57S/C101V/C282V mutant possessed the highest thermostability. The stabilizing mechanism of these mutations were elucidated by solving the structures of PpHDC C57S and C57S/C101V/C282V mutants by X-ray crystallography. In the crystal structures, two symmetry-related PpHDC molecules form a domain-swapped homodimer. The side chain of S57 is solvent exposed in the structure, indicating that the C57S mutation eliminates chemical oxidation or disulfide bond formation with a free thiol group, thereby providing greater stability. Residues 101 and 282 form hydrophobic interactions with neighboring hydrophobic residues. Mutations C101V and C282V enhanced thermostability of PpHDC by filling a cavity present in the hydrophobic core (C101V) and increasing hydrophobic interactions.

Technological roles of microorganisms in fish fermentation: a review

Fermentation is an important way to process and preserve fish. It not only gives the product a unique flavor and texture, but it also contributes to increased nutritional value and better functional properties. The production of fermented fish relies on naturally occurring enzymes (in the muscle or the intestinal tract) as well as microbial metabolic activity. This review focuses on the role of microorganisms on texture change, flavor formation, and biogenic amines accumulation in fermented fish. In addition, the production conditions and the major biochemical changes in fermented fish products are also introduced to help understand the factors influencing the quality of fermented fish. Moreover, prospects for further research of fermented fish are discussed.

Degradation of Histamine by Lactobacillus plantarum Isolated from Miso Products

Histamine is a toxic chemical and is the causative agent of food poisoning. This foodborne toxin may be degraded by the oxidative deamination activity of certain microorganisms. In this study, we isolated four histamine-degrading Lactobacillus plantarum bacteria from miso products. Among them, L. plantarum D-103 exhibited 100% degradation of histamine in de Man Rogosa Sharpe (MRS) broth containing 50 ppm of histamine after 24 h of incubation at 30°C. The optimal growth, histamine oxidase, and histamine-degrading activity of L. plantarum D-103 were observed in histamine MRS broth at pH 7.0, 3% NaCl, and 30°C. It also exhibited tolerance to broad ranges of pH (4 to 10) and salt concentrations (0 to 12%) in histamine MRS broth. Therefore, the histamine-degrading L. plantarum D-103 might be used as an additive culture to prevent histamine accumulation in miso products during fermentation.

Genomic and transcriptomic analyses of Agrobacterium tumefaciens S33 reveal the molecular mechanism of a novel hybrid nicotine-degrading pathway

Agrobacterium tumefaciens S33 is able to degrade nicotine via a novel hybrid of the pyridine and pyrrolidine pathways. It can be utilized to remove nicotine from tobacco wastes and transform nicotine into important functionalized pyridine precursors for some valuable drugs and insecticides. However, the molecular mechanism of the hybrid pathway is still not completely clear. Here we report the genome analysis of strain S33 and its transcriptomes grown in glucose-ammonium medium and nicotine medium. The complete gene cluster involved in nicotine catabolism was found to be located on a genomic island composed of genes functionally similar but not in sequences to those of the pyridine and pyrrolidine pathways, as well as genes encoding plasmid partitioning and replication initiation proteins, conjugal transfer proteins and transposases. This suggests that the evolution of this hybrid pathway is not a simple fusion of the genes involved in the two pathways, but the result of a complicated lateral gene transfer. In addition, other genes potentially involved in the hybrid pathway could include those responsible for substrate sensing and transport, transcription regulation and electron transfer during nicotine degradation. This study provides new insights into the molecular mechanism of the novel hybrid pathway for nicotine degradation.

Nicotine Dehydrogenase Complexed with 6-Hydroxypseudooxynicotine Oxidase Involved in the Hybrid Nicotine-Degrading Pathway in Agrobacterium tumefaciens S33

Nicotine, a major toxic alkaloid in tobacco wastes, is degraded by bacteria, mainly via pyridine and pyrrolidine pathways. Previously, we discovered a new hybrid of the pyridine and pyrrolidine pathways in Agrobacterium tumefaciens S33 and characterized its key enzyme 6-hydroxy-3-succinoylpyridine (HSP) hydroxylase. Here, we purified the nicotine dehydrogenase initializing the nicotine degradation from the strain and found that it forms a complex with a novel 6-hydroxypseudooxynicotine oxidase. The purified complex is composed of three different subunits encoded by ndhAB and pno, where ndhA and ndhB overlap by 4 bp and are ∼26 kb away from pno. As predicted from the gene sequences and from chemical analyses, NdhA (82.4 kDa) and NdhB (17.1 kDa) harbor a molybdopterin cofactor and two [2Fe-2S] clusters, respectively, whereas Pno (73.3 kDa) harbors an flavin mononucleotide and a [4Fe-4S] cluster. Mutants with disrupted ndhA or ndhB genes did not grow on nicotine but grew well on 6-hydroxynicotine and HSP, whereas the pno mutant did not grow on nicotine or 6-hydroxynicotine but grew well on HSP, indicating that NdhA and NdhB are responsible for initialization of nicotine oxidation. We successfully expressed pno in Escherichia coli and found that the recombinant Pno presented 2,6-dichlorophenolindophenol reduction activity when it was coupled with 6-hydroxynicotine oxidation. The determination of reaction products catalyzed by the purified enzymes or mutants indicated that NdhAB catalyzed nicotine oxidation to 6-hydroxynicotine, whereas Pno oxidized 6-hydroxypseudooxynicotine to 6-hydroxy-3-succinoylsemialdehyde pyridine. These results provide new insights into this novel hybrid pathway of nicotine degradation in A. tumefaciens S33.

Degradation of histamine by Bacillus polymyxa isolated from salted fish products

Histamine is the causative agent of scombroid poisoning, a foodborne chemical hazard. Histamine is degraded by the oxidative deamination activity of certain microorganisms. In this study, eight histamine-degrading bacteria isolated from salted fish products were identified as Rummeliibacillus stabekisii (1 isolate), Agrobacterium tumefaciens (1 isolate), Bacillus cereus (2 isolates), Bacillus polymyxa (1 isolate), Bacillus licheniformis (1 isolate), Bacillus amyloliquefaciens (1 isolate), and Bacillus subtilis (1 isolate). Among them, B. polymyxa exhibited the highest activity in degrading histamine than the other isolates. The ranges of temperature, pH, and salt concentration for growth and histamine degradation of B. polymyxa were 25–37°C, pH 5–9, and 0.5–5% NaCl, respectively. B. polymyxa exhibited optimal growth and histamine-degrading activity at 30°C, pH 7, and 0.5% NaCl in histamine broth for 24 hours of incubation. The histamine-degrading isolate, B. polymyxa, might be used as a starter culture in inhibiting histamine accumulation during salted fish product fermentation.

Crystallization and preliminary crystallographic analysis of histamine dehydrogenase from Natrinema gari BCC 24369

Histamine dehydrogenase (HADH) catalyzes the oxidative deamination of histamine, resulting in the production of imidazole acetaldehyde and an ammonium ion. The enzyme isolated from the newly identified halophilic archaeon Natrinema gari BCC 24369 is significantly different from the previously described protein from Nocardioides simplex. This newly identified HADH comprises three subunits with molecular weights of 49.0, 24.7 and 23.9 kDa, respectively, and is optimally active under high-salt conditions (3.5-5 M NaCl). As a step in the exploration of the unique properties of the protein, the HADH heterotrimer was purified and crystallized. Crystals were obtained using the sitting-drop vapor-diffusion method from a solution composed of 0.2 M calcium chloride dihydrate, 0.1 M HEPES pH 7.5, 28% PEG 400. Diffraction data were collected at -173°C to a resolution limit of 2.4 Å on the Southeast Regional Collaborative Access Team (SER-CAT) beamline 22-ID at the Advanced Photon Source, Argonne National Laboratory. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a=211.9, b=58.6, c=135.4 Å, β=103.0°. The estimated Matthews coefficient is 3.21 Å3 Da(-1), corresponding to 61.7% solvent content.

Stopped flow kinetic studies on reductive half-reaction of histamine dehydrogenase from Nocardioides simplex with histamine

Histamine dehydrogenase from Nocardioides simplex (HmDH) which catalyzes the oxidative deamination of histamine is an iron-sulphur-containing flavoprotein. For our further understanding on the intramolecular electron transfer process, the reductive half reaction of HmDH with histamine has been studied by stopped flow spectrophotometry at pH 7.5 and 10. The reaction at pH 7.5 is found to be analysed on a kinetic model composed of three sequential first-order reactions. The first fast phase, of which the rate constant shows a hyperbolic dependence on the histamine concentration, is assigned to a direct two-electron reduction of the oxidized flavin (CFMN(O)) by histamine with no involvement of the semiquinone form of the flavin (CFMN(S)). The second moderate process is the substrate-independent intramolecular single-electron transfer from the reduced flavin to the oxidized iron-sulphur cluster. The third slow process is considered to reflect the second binding of histamine to CFMN(S), which is responsible for the substrate inhibition. At pH 10, the reaction is analysed with one pseudo-first-order reaction phase which is substrate-dependent two-electron reduction of CFMN(O) coupled with the subsequent fast intersubunit single-electron transfer. The UV-vis spectroscopy of HmDH suggests the deprotonation of Tyr residues, which seems to cause the switching of the electron transfer property.

Scombroid poisoning: a review

Scombroid poisoning, also called histamine fish poisoning, is an allergy-like form of food poisoning that continues to be a major problem in seafood safety. The exact role of histamine in scombroid poisoning is not straightforward. Deviations from the expected dose-response have led to the advancement of various possible mechanisms of toxicity, none of them proven. Histamine action levels are used in regulation until more is known about the mechanism of scombroid poisoning. Scombroid poisoning and histamine are correlated but complicated. Victims of scombroid poisoning respond well to antihistamines, and chemical analyses of fish implicated in scombroid poisoning generally reveal elevated levels of histamine. Scombroid poisoning is unique among the seafood toxins since it results from product mishandling rather than contamination from other trophic levels. Inadequate cooling following harvest promotes bacterial histamine production, and can result in outbreaks of scombroid poisoning. Fish with high levels of free histidine, the enzyme substrate converted to histamine by bacterial histidine decarboxylase, are those most often implicated in scombroid poisoning. Laboratory methods and screening methods for detecting histamine are available in abundance, but need to be compared and validated to harmonize testing. Successful field testing, including dockside or on-board testing needed to augment HACCP efforts will have to integrate rapid and simplified detection methods with simplified and rapid sampling and extraction. Otherwise, time-consuming sample preparation reduces the impact of gains in detection speed on the overall analysis time.

N1,N12-diacetylspermine oxidase from Debaryomyces hansenii T-42: purification, characterization, molecular cloning and gene expression

An FAD-dependent N(1),N(12)-diacetylspermine oxidase (DASpmOX), which seems suitable for enzymatic determination of the tumor marker N(1),N(12)-diacetylspermine (DASpm), was isolated from Debaryomyces hansenii T-42. DASpmOX exhibited the most excellent specificity toward DASpm among all polyamine oxidases found to date, and the specificity for DASpm could be raised by adjusting the pH of the buffer and adding TritonX-100. In potassium phosphate (pH 7.0) with 0.3% TritonX-100, this enzyme did not have any detectable activity toward free polyamines, and the reaction rate of N(1),N(8)-diacetylspermidine, N(1)-acetylspermine, N(1)-acetylspermidine, and N(8)-acetylspermidine was only 19%, 7.8%, 7.8%, and 1.0% of that of DASpm, respectively. The gene encoding DASpmOX was cloned and expressed in Escherichia coli. The apparent k(cat) and K(m) values of recombinant enzyme for DASpm were found to be 158 s(-1) and 3.1 x 10(-4) M under the conditions described above, respectively.