CRYSTAL-STRUCTURE OF A FREE-RADICAL ENZYME, GALACTOSE-OXIDASE
CRYSTAL-STRUCTURE OF A FREE-RADICAL ENZYME, GALACTOSE-OXIDASE
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DOI：
10.1006/jmbi.1994.1335
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发表时间：
1994-05-20
影响因子：
5.6
通讯作者：
KNOWLES, PF
中科院分区：
文献类型：
--
作者：
ITO, N;PHILLIPS, SEV;KNOWLES, PF
含铜酶半乳糖氧化酶的晶体结构已通过多次同晶置换得到解析，并精确到1·7 μ m的分辨率。X射线结构揭示了一个独特的多肽折叠。该蛋白质可分为三个结构域，所有结构域几乎完全由β链组成。第二个结构域的结构特别引人注目，28条β链以假7重对称排列。铜位点位于蛋白质的表面，并且具有极其丰富的芳香族侧链。铜离子有两个组氨酸，两个酪氨酸，和一个外部配体在扭曲的四方锥配位。吡咯并喹啉醌作为GOase中共价结合的辅因子的存在已被排除。相反，已经观察到Tyr272和Cys228之间的意想不到的共价连接，其功能作用可能与Tyr272处酪氨酸自由基的存在有关。酪氨酸自由基可以通过离域到Cys228和与Trp290的堆积相互作用来稳定。底物结合的结构模型，提出了一个解释的酶和许多的光谱和酶学数据的底物特异性。虽然该模型目前缺乏直接的证实，但它应该为进一步的光谱学和晶体学研究提供刺激。
The crystal structure of the copper-containing enzyme, galactose oxidase, has been solved by multiple isomorphous replacement and refined to a resolution of 1·7 Å. The X-ray structure reveals a unique polypeptide fold. The protein can be divided into three domains, all of which consist almost entirely of β-strands. The structure of the second domain is particularly striking, 28 β-strands arranged in a pseudo 7-fold symmetry. The copper site is on the surface of the protein and extremely rich in aromatic side-chains. The copper ion has two histidine, two tyrosines, and one external ligand in distorted square pyramidal coordination. The presence of pyrroloquinoline quinone as a covalently bound cofactor in GOase has been excluded. Instead, an unexpected covalent linkage between Tyr272 and Cys228 has been observed, whose functional role may relate to the presence of a tyrosine free radical at Tyr272. The tyrosine free radical could be stabilized by delocalization to Cys228 and stacking interactions with Trp290. A structural model for substrate binding is proposed that offers an explanation for the substrate specificity of the enzyme and many of the spectroscopic and enzymological data. Although the model lacks direct confirmation at present, it should provide a stimulus for further spectroscopic and crystallographic studies.