Cytochrome b5 reductase–cytochrome b5 as an active P450 redox enzyme system in Phanerochaete chrysosporium: Atypical properties and in vivo evidence of electron transfer capability to CYP63A2

Two central redox enzyme systems exist to reduce eukaryotic P450 enzymes, the P450 oxidoreductase (POR) and the cyt b₅ reductase–cyt b₅. In fungi, limited information is available for the cyt b₅ reductase–cyt b₅ system. Here we characterized the kinetic mechanism of (cyt b₅r)–cyt b₅ redox system from the model white-rot fungus Phanerochaete chrysosporium (Pc) and made a quantitative comparison to the POR system. We determined that Pc-cyt b₅r followed a “ping-pong” mechanism and could directly reduce cytochrome c. However, unlike other cyt b₅ reductases, Pc-cyt b₅r lacked the typical ferricyanide reduction activity, a standard for cyt b₅ reductases. Through co-expression in yeast, we demonstrated that the Pc-cyt b₅r–cyt b₅ complex is capable of transferring electrons to Pc-P450 CYP63A2 for its benzo(a)pyrene monooxygenation activity and that the efficiency was comparable to POR. In fact, both redox systems supported oxidation of an estimated one-third of the added benzo(a)pyrene amount. To our knowledge, this is the first report to indicate that the cyt b₅r–cyt b₅ complex of fungi is capable of transferring electrons to a P450 monooxygenase. Furthermore, this is the first eukaryotic quantitative comparison of the two P450 redox enzyme systems (POR and cyt b₅r–cyt b₅) in terms of supporting a P450 monooxygenase activity.     

转哺乳动物cyp2e1基因烟草植株再生及其分析

哺乳动物肝细胞中cyp2e1基因所编码的蛋白CYP2E1在代谢异型有机物方面起着重要作用,转cyp2e1基因植物可以代谢多种小分子有机污染物;但cyp2e1基因在植物体内的表达调控和代谢机理尚不完全清楚。文中将含有cyp2e1基因的质粒pSLD50-6和对照gus基因的质粒pKH200转入根癌农杆菌GV3101,利用根癌农杆菌转基因技术将cyp2e1基因和对照gus基因成功转入烟草,分别获得了转cyp2e1和gus基因再生植株。选取PCR鉴定的再生植株进行荧光定量PCR(qRT-PCR)分析,结果表明:在转录水平上,转cyp2e1基因烟草中,乙醇处理后cyp2e1基因的表达明显下降,苯和甲苯处理后cyp2e1基因的表达量稍有下降;而丙酮、甲醛处理和缺氧条件下cyp2e1基因的表达有不同程度的升高。此外,苯处理后,转cyp2e1基因烟草中NADPH-P450氧化还原酶和细胞色素b5酶的基因活性显著提高,说明烟草中NADPH-P450氧化还原酶和细胞色素b5酶与CYP2E1酶的解毒过程有关,可能起到哺乳动物体内的NADPH-P450氧化还原酶和细胞色素b5的功能,参与CYP2E1酶催化过程的电子传递链。     

Bio-informatics based analysis of genes implicated in alcohol mediated liver injury

Alcohol induced liver injury has been studied extensively. Using literature search and bioinformatics tools, the present study characterizes the genes involved in alcohol induced liver injury. The cellular and metabolic processes in which genes involved in alcohol induced liver injury are implicated are also discussed. The genes related to alcohol induced liver injury are also involved in affecting certain molecular functions and metabolism of drugs, besides being associated with diseases. In conclusion, the changes in regulation of genes implicated in alcohol induced liver injury apart from causing alcohol mediated hepatic dysfunction may affect other vital processes in the body.     

Cytosolic thioredoxin system facilitates the import of mitochondrial small Tim proteins

Thiol‐disulphide redox regulation has a key role during the biogenesis of mitochondrial intermembrane space (IMS) proteins. Only the Cys‐reduced form of precursor proteins can be imported into mitochondria, which is followed by disulphide bond formation in the mitochondrial IMS. In contrast to the wealth of knowledge on the oxidation process inside mitochondria, little is known about how precursors are maintained in an import‐competent form in the cytosol. Here we provide the first evidence that the cytosolic thioredoxin system is required to maintain the IMS small Tim proteins in reduced forms and facilitate their mitochondrial import during respiratory growth.     

Isolation and expression of a Bacillus cereus gene encoding benzil reductase.

Benzil was reduced stereospecifically to (S)-benzoin by Bacillus cereus strain Tim-r01. To isolate the gene responsible for asymmetric reduction, we constructed a library consisting of Escherichia coli clones that harbored plasmids expressing Bacillus cereus genes. The library was screened using the halo formation assay, and one clone showed benzil reduction to (S)-benzoin. Thus, this clone seemed to carry a plasmid encoding a Bacillus cereus benzil reductase. The deduced amino acid sequence had marked homologies to the Bacillus subtilis yueD protein (41% identity), the yeast open reading frame YIR036C protein (31%), and the mammalian sepiapterin reductases (28% to 30%), suggesting that benzil reductase is a novel short-chain de-hydrogenases/ reductase.     

Insights into the binding of ferulic acid to the thermally treated xanthine oxidase

Ferulic acid (FA) is a biologically active compound used as an additive in the food industry, and possesses a wide range of therapeutic effects for treating different health problems. The interaction between FA and bovine xanthine oxidase (XOD) has been investigated by means of fluorescence spectroscopy methods. The numbers of binding sites and the binding constants were estimated at various temperatures and the results indicated the existence of one specific FA binding site of XOD. Detailed information on the interaction between molecules gathered after performing in silico molecular docking indicated the accommodation of the FA molecule in a XOD binding pocket, in close vicinity to the active site residues. The formation of the XOD–FA complex causes the quenching of protein fluorescence. The process followed a static mechanism at lower temperatures, and a dynamic mechanism at higher temperatures. The thermodynamic parameters calculated on the basis of different temperatures revealed that the association between FA and XOD is a spontaneous process driven by enthalpy and dominated by hydrogen bonding and van der Waals interaction. The results of synchronous fluorescence and 3D fluorescence spectra showed that the conformation of protein was altered in the presence of FA. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization of a HoxEFUYH type of [NiFe] hydrogenase from <Emphasis Type="Italic">Allochromatium vinosum</Emphasis> and some EPR and IR properties of the hydrogenase module

A soluble hydrogenase from Allochromatium vinosum was purified. It consisted of a large (M _r = 52 kDa) and a small (M _r = 23 kDa) subunit. The genes encoding for both subunits were identified. They belong to an open reading frame where they are preceded by three more genes. A DNA fragment containing all five genes was cloned and sequenced. The deduced amino acid sequences of the products characterized the complex as a member of the HoxEFUYH type of [NiFe] hydrogenases. Detailed sequence analyses revealed binding sites for eight Fe–S clusters, three [2Fe–2S] clusters and five [4Fe–4S] clusters, six of which are also present in homologous subunits of [FeFe] hydrogenases and NADH:ubiquione oxidoreductases (complex I). This makes the HoxEFUYH type of hydrogenases the one that is evolutionary closest to complex I. The relative positions of six of the potential Fe–S clusters are predicted on the basis of the X-ray structures of the Clostridium pasteurianum [FeFe] hydrogenase I and the hydrophilic domain of complex I from Thermus thermophilus. Although the HoxF subunit contains binding sites for flavin mononucleotide and NAD(H), cell-free extracts of A. vinosum did not catalyse a H₂-dependent reduction of NAD⁺. Only the hydrogenase module (HoxYH) could be purified. Its electron paramagnetic resonance (EPR) and IR spectral properties showed the presence of a Ni–Fe active site and a [4Fe–4S] cluster. Its activity was sensitive to carbon monoxide. No EPR signals from a light-sensitive Ni_a–C* state could be observed. This study presents the first IR spectroscopic data on the HoxYH module of a HoxEFUYH type of [NiFe] hydrogenase.