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首页> 美国卫生研究院文献>Wiley-Blackwell Online Open >The structure function and properties of sirohaem decarboxylase - an enzyme with structural homology to a transcription factor family that is part of the alternative haem biosynthesis pathway
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The structure function and properties of sirohaem decarboxylase - an enzyme with structural homology to a transcription factor family that is part of the alternative haem biosynthesis pathway

机译：sirohaem脱羧酶的结构功能和特性-一种与转录因子家族具有结构同源性的酶是另一种haem生物合成途径的一部分

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摘要

Some bacteria and archaea synthesize haem by an alternative pathway, which involves the sequestration of sirohaem as a metabolic intermediate rather than as a prosthetic group. Along this pathway the two acetic acid side-chains attached to C12 and C18 are decarboxylated by sirohaem decarboxylase, a heterodimeric enzyme composed of AhbA and AhbB, to give didecarboxysirohaem. Further modifications catalysed by two related radical SAM enzymes, AhbC and AhbD, transform didecarboxysirohaem into Fe-coproporphyrin III and haem respectively. The characterization of sirohaem decarboxylase is reported in molecular detail. Recombinant versions of Desulfovibrio desulfuricans, Desulfovibrio vulgaris and Methanosarcina barkeri AhbA/B have been produced and their physical properties compared. The D. vulgaris and M. barkeri enzyme complexes both copurify with haem, whose redox state influences the activity of the latter. The kinetic parameters of the D. desulfuricans enzyme have been determined, the enzyme crystallized and its structure has been elucidated. The topology of the enzyme reveals that it shares a structural similarity to the AsnC/Lrp family of transcription factors. The active site is formed in the cavity between the two subunits and a AhbA/B-product complex with didecarboxysirohaem has been obtained. A mechanism for the decarboxylation of the kinetically stable carboxyl groups is proposed.
机译：一些细菌和古细菌通过另一种途径合成血红素，其中包括将西罗海藻作为一种代谢中间体而不是一个假肢进行隔离。沿着该途径，连接到C12和C18的两条乙酸侧链被西罗汉脱羧酶（一种由AhbA和AhbB组成的异二聚酶）脱羧，生成二脱羧西罗汉。由两种相关的自由基SAM酶AhbC和AhbD催化的进一步修饰分别将二脱羧西罗哈姆转化为Fe-coproporphyrin III和haem。西罗海姆脱羧酶的表征已在分子细节中报道。已生产了脱硫脱硫弧菌，寻常脱硫弧菌和巴氏甲烷菌的重组体AhbA / B，并比较了它们的物理性质。寻常小球藻和巴氏支原体酶复合物均与血红素共纯化，血红素的氧化还原状态影响后者的活性。已经确定了脱硫尿链霉菌酶的动力学参数，使该酶结晶并阐明了其结构。该酶的拓扑结构表明它与转录因子AsnC / Lrp家族具有相似的结构。活性位点在两个亚基之间的空腔中形成，并获得了具有二脱羧西罗海姆的AhbA / B产物复合物。提出了动力学稳定的羧基脱羧的机理。

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