A new scaffold for binding haem in the cytochrome domain of the extracellular flavocytochrome cellobiose dehydrogenase
A new scaffold for binding haem in the cytochrome domain of the extracellular flavocytochrome cellobiose dehydrogenase
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DOI：
10.1016/s0969-2126(00)00082-4
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发表时间：
2000-01-15
期刊：
影响因子：
--
通讯作者：
Divne, C
中科院分区：
文献类型：
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作者：
Hallberg, BM;Bergfors, T;Divne, C
背景资料：真菌氧化还原酶纤维二糖脱氢酶（CDH）降解木质素和纤维素，是唯一已知的细胞外黄细胞色素。这种haemoflavoenzyme有一个多结构域的组织与b型细胞色素结构域连接到一个大的黄素脱氢酶结构域。这两个结构域可以通过蛋白水解分离以产生功能性细胞色素和黄素脱氢酶。在这里，我们报告的CDH的细胞色素结构域的晶体结构。结果：从木材降解真菌黄孢原毛平革菌CDH的b型细胞色素结构域的晶体结构已确定在1.9埃分辨率使用多个同晶置换，包括异常散射信息。三种模型的细胞色素已被完善：在体外制备的细胞色素在其氧化还原非活性状态（pH 7.5）和氧化还原活性状态（pH 4.6），以及天然存在的细胞色素fragment.Conclusions：190个残基长的CDH细胞色素结构域折叠作为一个β三明治的抗体Fab V-H结构域的拓扑结构。血红素铁由Met 65和His 163连接，这证实了以前的光谱研究结果。这仅仅是具有这种连接的b型细胞色素的第二个实例，第一个是细胞色素B（562）。半丙酸基团的表面暴露，因此，可能发挥作用的细胞色素和黄素蛋白结构域之间的关联，并在域间电子转移。与失活形式相比，在氧化还原活性pH下细胞色素的总体结构没有太大差异，这排除了部分变性导致pH依赖性氧化还原失活的可能性。从天然存在的细胞色素的电子密度图，我们得出结论，它对应于蛋白水解制备的细胞色素结构域。
Background: The fungal oxidoreductase cellobiose dehydrogenase (CDH) degrades both lignin and cellulose, and is the only known extracellular flavocytochrome. This haemoflavoenzyme has a multidomain organisation with a b-type cytochrome domain linked to a large flavodehydrogenase domain. The two domains can be separated proteolytically to yield a functional cytochrome and a flavodehydrogenase. Here, we report the crystal structure of the cytochrome domain of CDH.Results: The crystal structure of the b-type cytochrome domain of CDH from the wood-degrading fungus Phanerochaete chrysosporium has been determined at 1.9 Angstrom resolution using multiple isomorphous replacement ncluding anomalous scattering information. Three models of the cytochrome have been refined: the in vitro prepared cytochrome in its redox-inactive state (pH 7.5) and redox-active state (pH 4.6), as well as the naturally occurring cytochrome fragment.Conclusions: The 190-residue long cytochrome domain of CDH folds as a beta sandwich with the topology of the antibody Fab V-H domain. The haem iron is ligated by Met65 and His 163, which confirms previous results from spectroscopic studies. This is only the second example of a b-type cytochrome with this ligation, the first being cytochrome b(562). The haem-propionate groups are surface exposed and, therefore, might play a role in the association between the cytochrome and flavoprotein domain, and in interdomain electron transfer. There are no large differences in overall structure of the cytochrome at redoxactive pH as compared with the inactive form, which excludes the possibility that pH-dependent redox inactivation results from partial denaturation. From the electron-density map of the naturally occurring cytochrome, we conclude that it corresponds to the proteolytically prepared cytochrome domain.