X-RAY CRYSTAL-STRUCTURE OF CANINE MYELOPEROXIDASE AT 3 ANGSTROM RESOLUTION
X-RAY CRYSTAL-STRUCTURE OF CANINE MYELOPEROXIDASE AT 3 ANGSTROM RESOLUTION
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DOI：
10.1016/0022-2836(92)90133-5
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发表时间：
1992-07-05
影响因子：
5.6
通讯作者：
FENNA, RE
中科院分区：
文献类型：
--
作者：
ZENG, J;FENNA, RE
髓过氧化物酶的三维结构已通过X射线晶体学测定到3 μ m分辨率。两个重原子衍生物被用来相位初始多个同晶置换映射，随后通过溶剂平坦化和非晶体学对称性平均来改进。晶体学精修给出了最终模型，其R因子为0.257。键长和键角与理想值的均方根偏差分别为0.011 °和3.8 °。两个明显相同的半分子通过局部二联体联系在一起，并通过一个二硫键共价连接。每个半分子由108和466个氨基酸残基的两条多肽链、血红素辅基、结合的钙离子和至少三个天冬酰胺连接的糖基化位点组成。有六个额外的链内二硫键，五个在大多肽中，一个在小多肽中。包括血红素结合位点的中心核心区由五个α-螺旋组成。围绕这个核心的较大多肽区域被组织成局部折叠的结构域，其中二级结构主要是α-螺旋，很少有组织的β-折叠。在血红素的远端侧，组氨酸95和精氨酸239可能直接参与催化机制，以类似于非同源酶细胞色素过氧化物酶的远端组氨酸和精氨酸的方式。与血红素共价连接的位点已被初步确定为谷氨酸242，尽管该连接的化学性质仍不确定。髓过氧化物酶是哺乳动物过氧化物酶家族的一员，包括甲状腺过氧化物酶、嗜酸性粒细胞过氧化物酶和乳过氧化物酶。血红素环境，定义我们的模型髓过氧化物酶，似乎是高度保守的这四种哺乳动物过氧化物酶。此外，保守的所有12个半胱氨酸残基参与的6个链内二硫键和钙结合环表明，该基因家族的成员的三维结构很可能是非常相似的。
The three-dimensional structure of the enzyme myeloperoxidase has been determined by X-ray crystallography to 3 Å resolution. Two heavy atom derivatives were used to phase an initial multiple isomorphous replacement map that was subsequently improved by solvent flattening and non-crystallographic symmetry averaging. Crystallographic refinement gave a final model with anR-factor of 0.257. The root-mean-square deviations from ideality for bond lengths and angles were 0.011 Å and 3.8 °.Two, apparently identical, halves of the molecule are related by local dyad and covalently linked by a single disulfide bridge. Each half-molecule consists of two polypeptide chains of 108 and 466 amino acid residues, a heme prosthetic group, a bound calcium ion and at least three sites of asparagine-linked glycosylation. There are six additional intra-chain disulfide bonds, five in the large polypeptide and one in the small. A central core region that includes the heme binding site is composed of five α-helices. Regions of the larger polypeptide surrounding this core are organized into locally folded domains in which the secondary structure is predominantly α-helical with very little organized β-sheet.A proximal ligand to the heme iron atom has been identified as histidine 336, which is in turn hydrogen-bonded to asparagine 421. On the distal side of the heme, histidine 95 and arginine 239 are likely to participate directly in the catalytic mechanism, in a manner analogous to the distal histidine and arginine of the non-homologous enzyme cytochromecperoxidase. The site of the covalent linkage to the heme has been tentatively identified as glutamate 242, although the chemical nature of the link remains uncertain. The calcium binding site has been located in a loop comprising residues 168 to 174 together with aspartate 96.Myeloperoxidase is a member of a family of homologous mammalian peroxidases that includes thyroid peroxidase, eosinophil peroxidase and lactoperoxidase. The heme environment, defined by our model for myeloperoxidase, appears to be highly conserved in these four mammalian peroxidases. Furthermore, the conservation of all 12 cysteine residues involved in the six intra-chain disulfide bonds and the calcium binding loop suggests that the three-dimensional structures of members of this gene family are likely to be quite similar.