Protein dynamics: Imidazole binding to class I c-type cytochromes
Protein dynamics: Imidazole binding to class I c-type cytochromes
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DOI：
10.1006/abbi.1999.1440
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发表时间：
1999-11-15
影响因子：
3.9
通讯作者：
Cusanovich, MA
中科院分区：
文献类型：
--
作者：
Dumortier, C;Meyer, TE;Cusanovich, MA
紫色光养细菌球形红杆菌和胶囊红杆菌的氧化细胞色素c(2)与咪唑类中性物质的结合强度(K-a=1440+/-40M-1)是马线粒体细胞色素c(K-a=30+/-1M-1)的50倍。咪唑结合动力学与三种蛋白质在高配基浓度下限速步长的变化一致。这归因于在咪唑结合之前导致铁-蛋氨酸键断裂的构象变化。Rb，sphaeroids细胞色素c(2)咪唑络合物(Axelrod ct at，Acta Crystalogr，D50,596-602)的三维结构支持这样的观点，即构象变化基本上局限于连接的蛋氨酸两侧的大约7个残基，并且Phe 102羰基、内部水和结合的咪唑之间存在氢键。细胞色素c(2)这一区域的插入和缺失，蛋氨酸附近的一个脯氨酸的存在，以及马细胞色素c动态区域的较小尺寸，表明马细胞色素c中不存在稳定的氢键，因此，对咪唑的亲和力存在显著差异。配体结合的动力学与铁-蛋氨酸键的强度(由695 nm吸收带的pk测量)或所研究的细胞色素的整体稳定性无关。然而，两种细胞色素c(2)与咪唑的结合性质非常相似，表明Rb。球藻细胞色素c(2)-咪唑络合物结构是研究相应Rb的良好模型。囊状细胞色素c(2)复合体。值得注意的是，在整个进化过程中，连接的蛋氨酸附近的肽链的运动一直被保存下来，这表明它在C型细胞色素的功能中发挥了作用。(C)1999年学术出版社。
The oxidized cytochrome c(2) from the purple phototrophic bacteria, Rhodobacter sphaeroides and Rhodobacter capsulatus, bind the neutral species of imidazole (K-a = 1440 +/- 40 M-1) 50 times more strongly than does horse mitochondrial cytochrome c (K-a = 30 +/- I M-1). The kinetics of imidazole binding are consistent with a change in rate-limiting step at; high ligand concentrations for all three proteins. This is attributed to a conformational change leading to breakage of the iron-methionine bond which precedes imidazole binding. The three-dimensional structure of the Rb, sphaeroides cytochrome c(2) imidazole complex (Axelrod ct at, Acta Crystalogr, D50, 596-602) supports the view that the conformational changes are essentially localized to approximately seven residues on either side of the ligated methionine and there is a hydrogen bond between the Phe 102 carbonyl, an internal water, and the bound imidazole. Insertions and deletions in this region of cytochrome c(2), the presence of a proline near the methionine, and the smaller size of the dynamic region of horse cytochrome c suggest that the stabilizing hydrogen bond is not present in horse cytochrome c, hence, the dramatic difference in affinity for imidazole. The kinetics of ligand binding do not correlate with either the strength of the iron-methionine bond as measured by the pK of the 695-nm absorption band or the overall stability of the cytochromes studied. However, the very similar imidazole binding properties of the two cytochromes c(2) indicate that the Rb. sphaeroides cytochrome c(2)-imidazole complex structure is an excellent model for the corresponding Rb. capsulatus cytochrome c(2) complex. It is notable that the movement of the peptide chain in the vicinity of the ligated methionine has been preserved throughout evolution and suggests a role in the function of c-type cytochromes. (C) 1999 Academic Press.