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首页> 外文期刊>Acta crystallographica.Section D Biological crystallography. >Structural evidence for the partially oxidized dipyrromethene and dipyrromethanone forms of the cofactor of porphobilinogen deaminase: Structures of the Bacillus megaterium enzyme at near-atomic resolution
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Structural evidence for the partially oxidized dipyrromethene and dipyrromethanone forms of the cofactor of porphobilinogen deaminase: Structures of the Bacillus megaterium enzyme at near-atomic resolution

机译：结构的证据部分氧化dipyrromethene和dipyrromethanone形式的胆色素原脱氨酶的辅因子:结构的芽孢杆菌在near-atomic megaterium酶决议

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The enzyme porphobilinogen deaminase (PBGD; hydroxymethylbilane synthase; EC 2.5.1.61) catalyses an early step of the tetrapyrrole-biosynthesis pathway in which four molecules of the monopyrrole porphobilinogen are condensed to form a linear tetrapyrrole. The enzyme possesses a dipyrromethane cofactor, which is covalently linked by a thioether bridge to an invariant cysteine residue (Cys241 in the Bacillus megaterium enzyme). The cofactor is extended during the reaction by the sequential addition of the four substrate molecules, which are released as a linear tetrapyrrole product. Expression in Escherichia coli of a His-tagged form of B. megaterium PBGD has permitted the X-ray analysis of the enzyme from this species at high resolution, showing that the cofactor becomes progressively oxidized to the dipyrromethene and dipyrromethanone forms. In previously solved PBGD structures, the oxidized cofactor is in the dipyromethenone form, in which both pyrrole rings are approximately coplanar. In contrast, the oxidized cofactor in the B. megaterium enzyme appears to be in the dipyrromethanone form, in which the C atom at the bridging α-position of the outer pyrrole ring is very clearly in a tetrahedral configuration. It is suggested that the pink colour of the freshly purified protein is owing to the presence of the dipyrromethene form of the cofactor which, in the structure reported here, adopts the same conformation as the fully reduced dipyrromethane form.
机译：这种酶胆色素原脱氨酶(PBGD;hydroxymethylbilane合酶;催化作用的早期步骤tetrapyrrole-biosynthesis四个途径分子的monopyrrole胆色素原凝聚,形成一个线性四吡咯。酶具有dipyrromethane代数余子式,共价相连的硫醚桥不变的半胱氨酸残基(Cys241芽孢杆菌megaterium酶)。在反应的连续扩展添加四个底物分子,被释放的线性四吡咯产品。His-tagged表达大肠杆菌形式的b megaterium PBGD允许从这个物种的x射线分析酶代数余子式的高分辨率,显示逐渐的被氧化的dipyrromethene和dipyrromethanone形式。以前解决PBGD结构,氧化了代数余子式的dipyromethenone形式,吡咯环都是大约共面。相反,氧化辅因子的B。megaterium酶似乎在dipyrromethanone形式,C原子的桥接外吡咯环的α-安置很显然一个四面体配置。建议新鲜的粉色纯化蛋白是由于的存在dipyrromethene代数余子式的形式,报告结构,采用相同的构象完全dipyrromethane减少的形式。

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