CRYSTAL-STRUCTURE OF ABRIN-A AT 2.14 ANGSTROM
CRYSTAL-STRUCTURE OF ABRIN-A AT 2.14 ANGSTROM
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DOI：
10.1006/jmbi.1995.0382
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发表时间：
1995-07-14
影响因子：
5.6
通讯作者：
LIN, JY
中科院分区：
文献类型：
--
作者：
TAHIROV, TH;LU, TH;LIN, JY
用分子置换法测定了相思豆毒蛋白-a的晶体结构。相思豆毒蛋白-a是一种Ⅱ型核糖体失活蛋白，来自于相思豆种子。该结构已在2.14埃下细化至18.9%的R因子。键长和键角与标准值的均方根偏差分别为0.013埃和1.82度。整体蛋白质折叠类似于蓖麻毒素，但在二级结构上存在差异，主要是A链。分子表面的几个部分差异很大，其中一些非常接近活性位点裂缝，可能会影响核糖体识别。除了Tyr 74的位置之外，不变活性位点残基的位置保持相同。两个水分子的氢键活性位点残基已被定位在活性位点裂缝。这两种酶都可能是水解N-C糖苷键的酶。目前的相思豆毒素a结构是无乳糖的;这可能是相思豆毒素a结晶所必需的。B链是一种糖蛋白，并确定了与早期预测的糖基化位点连接的两条糖链的几个糖残基的位置。其中一条糖链是两个相邻分子之间的桥，因为它的一个甘露糖残基连接到相邻分子的半乳糖结合位点。另一条糖链覆盖在B链的表面。
The crystal structure of abrin-a, a type II ribosome-inactivating protein from the seeds of Abrus precatorius, has been determined from a novel crystalline form by the molecular replacement method using the coordinates of ricin. The structure has been refined at 2.14 Angstrom to a R-factor of 18.9%. The root-mean-square deviations of bond lengths and angles from the standard values are 0.013 Angstrom and 1.82 degrees, respectively. The overall protein folding is similar to that of ricin, but there are differences in the secondary structure, mostly of the A-chain. Several parts of the molecular surface differ significantly; some of them are quite near the active site cleft, and probably influence ribosome recognition. The positions of invariant active site residues remain the same, except the position of Tyr74. Two water molecules of hydrogen-bonded active site residues have been located in the active site cleft. Both of them may be responsible for hydrolyzing the N-C glycosidic bond. The current abrin-a structure is lactose free; this is probably essential for abrin-a crystallization. The B-chain is a glycoprotein, and the positions of several sugar residues of two sugar chains linked to earlier predicted glycosylation sites were determined. One of the sugar chains is a bridge between two neighboring molecules, since one of its mannose residues is connected to the galactose binding site of the neighboring molecule. Another sugar chain covers the surface of the B-chain.