Tomohide Uno

Cytochrome P450 (CYP) in fish.

Cytochrome P450 (CYP) enzymes are members of the hemoprotein superfamily, and are involved in the mono-oxygenation reactions of a wide range of endogenous and exogenous compounds in mammals and plants. Characterization of CYP genes in fish has been carried out intensively over the last 20 years. In Japanese pufferfish (Takifugu rubripes), 54 genes encoding P450s have been identified. Across all species of fish, 137 genes encoding P450s have been identified. These genes are classified into 18 CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP5, CYP7, CYP8, CYP11, CYP17, CYP19, CYP20, CYP21, CYP24, CYP26, CYP27, CYP39, CYP46 and CYP51.We pinpointed eight CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP11, CYP17, CYP19 and CYP26 in this review because these CYP families are studied in detail. Studies of fish P450s have provided insights into the regulation of P450 genes by environmental stresses including water pollution. In this review, we present an overview of the CYP families in fish.

Functional analysis of the cucumisin propeptide as a potent inhibitor of its mature enzyme

Cucumisin is a subtilisin-like serine protease (subtilase) that is found in the juice of melon fruits (Cucumis melo L.). It is synthesized as a preproprotein consisting of a signal peptide, NH2-terminal propeptide, and 67-kDa protease domain. We investigated the role of this propeptide (88 residues) in the cucumisin precursor. Complementary DNAs encoding the propeptides of cucumisin, two other plant subtilases (Arabidopsis ARA12 and rice RSP1), and bacterial subtilisin E were expressed in Escherichia coli independently of their mature enzymes. The cucumisin propeptide strongly inhibited cucumisin in a competitive manner with a Ki value of 6.2 ± 0.55 nm. Interestingly, cucumisin was also strongly inhibited by ARA12 and RSP1 propeptides but not by the subtilisin E propeptide. In contrast, the propeptides of cucumisin, ARA12, and RSP1 did not inhibit subtilisin. Deletion analysis clearly showed that two hydrophobic regions, Asn32–Met38 and Gly97–Leu103, in the cucumisin propeptide were important for its inhibitory activity. Site-directed mutagenesis also confirmed the role of a Val36-centerd hydrophobic cluster within the Asn32–Met38 region in cucumisin inhibition. Circular dichroism spectroscopy revealed that the cucumisin propeptide had a secondary structure without a cognate protease domain and that the thermal unfolding of the propeptide at 90 °C was only partial and reversible. A tripeptide, Ile35-Val36-Tyr37, in the Asn32–Met38 region was thought to contribute toward the formation of a proper secondary structure necessary for cucumisin inhibition. This is the first report on the function and structural information of the propeptide of a plant serine protease.

Characteristics of Psychrophilic Alkaline Phosphatase

The phosphatase of a psychrophile (Shewanella sp.) was purified by ammonium sulfate fractionation, followed by sequential column chromatographies. The purified enzyme was electrophoretically homogeneous on native- and SDS-PAGE. Its molecular weight was 41,826 by its amino acid composition. The enzyme had its optimal pH for the activity at 9.8, and a broad substrate specificity to dephosphorylate ATP, pyrophosphate, glycerophosphate, and so on. Its activity was increased by metal ions including Mg(2+), Mn(2+), and Co(2+). The maximal activity was observed at 40°C, and the enzyme at 0°C showed 39% of activity at 40°C. The enzyme, however, tended to lose its activity at 20°C and pH 9.8. These results indicated that purified enzyme was an alkaline phosphatase with characteristics; high catalytic efficiency at low temperature and gradual inactivation at an intermediate temperature.

Rice Bifunctional α-Amylase/Subtilisin Inhibitor : Cloning and Characterization of the Recombinant Inhibitor Expressed in Escherichia coli

The complete nucleotide sequences of the cDNA and its gene that encode a bifunctional α-amylase/subtilisin inhibitor of rice (Oryza sativa L.) (RASI) were analyzed. RASI cDNA (939 bp) encoded a 200-residue polypeptide with a molecular mass of 21,417 Da, including a signal peptide of 22 amino acids. Sequence comparison and phylogenetic analysis showed that RASI is closely related to α-amylase/subtilisin inhibitors from barley and wheat. RASI was found to be expressed only in seeds, suggesting that it has a seed-specific function. A coding region of RASI cDNA without the signal peptide was introduced into Escherichia coli and was expressed as a His-tagged protein. Recombinant RASI was purified to homogeneity in a single step by Ni-chelating affinity column chromatography and characterized to elucidate the target enzyme. The recombinant inhibitor had strong inhibitory activity toward subtilisin, with an equimolar relationship, comparable with that of native RASI, and weak inhibitory activity toward some microbial α-amylases, but not toward animal or insect α-amylases. These results suggest that RASI might function in the defense of the seed against microorganisms.

Relationship between the expression of Rab family GTPases and neuropeptide hormones in the brain of Bombyx mori.

Rab proteins are small GTPases that play essential roles in vesicle transport. In this study, we examined the expression of Rab proteins and neuropeptide hormones in the brain of the silkworm, Bombyx mori. We produced antibodies against B. mori Rab1 and Rab14 in rabbits. Immunoblotting of samples of brain tissue from B. mori revealed a single band for each antibody. Rab1 and Rab14 immunohistochemical labeling in the brain of B. mori was restricted to neurons of the pars intercerebralis and dorsolateral protocerebrum. Rab1, Rab7 and Rab14 co-localized with bombyxin. Rab1 and Rab7 co-localized with eclosion hormone. Rab1 co-localized with prothoracicotropic hormone. These results suggest that Rab1, Rab7 and Rab14 may be involved in neuropeptide transport in the brain of B. mori. This is the first report on the specificity of Rab proteins for the secretion of different neuropeptides in insects.

Bioconversion of small molecules by cytochrome P450 species expressed in Escherichia coli

P450 (cytochrome P450) enzymes catalyse the mono‐oxygenation of a wide range of compounds such as steroids, fatty acids, vitamins and drugs. In the present paper we demonstrate a system for bioconverting diverse compounds [flavanone, DHEA (dehydroepiandrosterone) and 7‐ethoxycoumarin] using P450 species expressed in Escherichia coli. First, we expressed four P450 species: rabbit CYP2B (P450 family 2, subfamily B), fruitfly (Drosophila) CYP317A, rat CYP3A23 and mouse CYP2J5. Next, we added substrates directly to the incubation medium. The resulting metabolites were extracted and analysed by HPLC and spectrofluorimetry. The first substrate, 7‐ethoxycoumarin, was de‐ethylated by CYP2B; CYP2J5 and CYP3A23 showed weak activity, and CYP317A had no activity for 7‐ethoxycoumarin. We next used flavanone, a flavonoid, as a substrate for these four P450 species and other P450 species expressed previously. As a result, CYP2B, CYP2C43 and CYP2C29 catalysed flavanone 2‐hydroxylation. CYP2A5 catalysed 2‐ and 4‐hydroxylations. Finally, to produce diverse modified compounds, variants of CYP2A5 with point mutations were incubated with a steroid (DHEA) and an antioxidant (flavanone) in vivo. HPLC analysis indicated that two P450 species produced a 7‐β‐hydroxy‐DHEA and two P450 species produced a 2‐α‐hydroxy‐DHEA. Four P450 species catalysed flavanone 2‐ and 4‐hydroxylations. These results indicate that bioconversion by P450 is a useful technique to modify small molecules (steroids, coumarin and flavanone) and produce new, diverse hydroxylated compounds, which could be used for high‐throughput screening for drug discovery.

Small GTP-binding proteins in the brain-corpus cardiacum-corpus allatum complex of the silkworm, Bombyx mori: Involvement in the secretion of prothoracicotropic hormone

At least three GTP-binding proteins (G-proteins), 28, 25, and 21 kDa, were found in the brain-corpus cardiacum-corpus allatum complex (BR-CC-CA) of the silkworm, Bombyx mori. They bound to GTP and GDP specifically among nucleotides tested, indicating that these proteins are small G-proteins. The 25 kDa G-protein showed a cross-reactivity to anti-rab3A antibody, while it did not cross-react with anti-rhoA, rab3B, and anti-ras antibodies. On the other hand, the 28 and 21 kDa G-proteins showed no cross-reactivity to any of those antibodies tested. Immunoblot analysis using the anti-rab3A antibody demonstrated that the 25 kDa G-protein was detected preferentially in the BR-CC-CA, and to some extent in the suboesophageal ganglion, but not in the salivary gland, fat body, prothoracic gland, and oesophagus. These results suggested that the 25 kDa G-protein was a member of the rab family of G-proteins. Furthermore, 1 mM GTP gamma S capable of activating G-proteins induced BR-CC-CA to release PTTH under the conditions that stimulation of the PTTH release with hetero-trimeric G-protein was suppressed. These results indicated that the small G-proteins may possibly contribute to PTTH release in Bombyx mori.

The effects of single nucleotide polymorphisms in CYP2A13 on metabolism of 5-methoxypsoralen

A number of studies have demonstrated that cytochrome P450 (P450) converts furanocoumarin derivatives into reactive molecules, which form covalent bonds to biomolecules. 5-Methoxypsoralen (5-MOP) is a natural furanocoumarin from apiaceous plants. In this study, we examined the effect on 5-MOP metabolism of single nucleotide polymorphisms (SNPs) in CYP2A13. We used Escherichia coli-generated recombinant enzymes of wild-type CYP2A13*1 and five variants, CYP2A13*4 (R101Q), CYP2A13*5 (F453Y), CYP2A13*6 (R494C), CYP2A13*8 (D158E), and CYP2A13*9 (V323L). In high-performance liquid chromatography analyses of 5-MOP metabolic products, CYP2A13*1 converted 5-MOP into 5-MOP dihydrodiol; Km and Vmax values of the reaction were 1.44 ± 0.17 μM and 4.23 ± 0.36 nmol/(min · nmol P450), respectively. The generation of a dihydrodiol from 5-MOP implies that conversion by CYP2A13 causes toxicity due to the formation of covalent bonds with DNA or proteins. Most of the CYP2A13 variants could metabolize 5-MOP; Km values for CYP2A13*5, *6, *8, and *9 were 1.63 ± 0.12, 1.36 ± 0.10, 0.85 ± 0.09, and 0.58 ± 0.06 μM, respectively, and Vmax values were 3.20 ± 0.13, 4.69 ± 0.13, 2.34 ± 0.07, and 1.84 ± 0.09 nmol/(min · nmol P450), respectively. However, the processing of 5-MOP by CYP2A13*4 was not detectable. Based on this data, we hypothesize that SNPs within the CYP2A13 gene affect metabolism of 5-MOP in humans.

Putative regulatory mechanism of prothoracicotropic hormone (PTTH) secretion in the American cockroach, Periplaneta americana as inferred from co-localization of Rab8, PTTH, and protein kinase C in neurosecretory cells

Small GTPases of the Rab family act as essential regulators of vesicle transport pathways, including the exocytosis of neurohormones. These processes are not well-understood in insects. To address the physiological function of Rab proteins and their phosphorylation in insect neurosecretion, Rab8-like, prothoracicotropic hormone (PTTH)-like, and protein kinase C (PKC)-like immunohistochemical reactivities (-ir) were investigated in the brain of the American cockroach, Periplaneta americana. All the antibodies tested reacted with neurons in the pars intercerebralis, corpora cardiaca, and nervi corporis allati I. Double-labeling experiments demonstrated that all PTTH-ir were colocalized with Rab8-ir and PKC-ir in the pars intercerebralis, although exclusive reactivity was present to antisera against Rab8 or PKC. These findings support the notion that Rab8-like antigen is phosphorylated by PKC, and that this phosphorylation is involved in the axonal transport and secretion of PTTH in this species.

Metabolism of 7‐ethoxycoumarin, safrole, flavanone and hydroxyflavanone by cytochrome P450 2A6 variants

CYP 2A6 is a human enzyme that metabolizes many xenobiotics including coumarin, indole, nicotine and carcinogenic nitrosamines. The gene for CYP2A6 is polymorphic. There are few data available to clarify the relationship between P450 genetic variants and the metabolism of materials in food. The CYP 2A6 wild‐type protein and 13 mutants (CYP2A6.1, CYP2A6.2, CYP2A6.5, CYP2A6.6, CYP2A6.7, CYP2A6.8, CYP2A6.11, CYP2A6.15, CYP2A6.16, CYP2A6.17, CYP2A6.18, CYP2A6.21, CYP2A6.23 and CYP2A6.25) were co‐expressed with NADPH‐cytochrome P450 reductase in E. coli. The hydroxylase activities toward 7‐ethoxycoumarin, coumarin, safrole, flavanone and hydroxyflavanone were examined. Ten types of CYP2A6 variants except for CYP2A6.2, CYP2A6.5 and CYP2A6.6 showed Soret peaks (450 nm) typical of P450 in the reduced CO‐difference spectra and had 7‐ethoxycoumarin O‐deethylase activities. CYP2A6.15 and CYP2A6.18 showed higher activities for safrole 1′‐hydroxylation than CYP2A6.1. CYP2A6.25 and CYP2A6.7 had lower safrole 1′‐hydroxylase activities. CYP2A6.7 had lower flavanone 6‐ and 2′‐hydroxylase activities, whereas CYP2A6.25 had higher 6‐hydroxylase activity and lower 2′‐hydroxylase activity. Hydroxyflavanone was metabolized by CYP2A6.25, but was not metabolized by wild‐type CYP2A6.1. These results indicate that CYP2A6.25 possessed new substrate specificity toward flavonoids. Copyright