The structure of rhamnose isomerase from Escherichia coli and its relation with xylose isomerase illustrates a change between inter and intra-subunit complementation during evolution
The structure of rhamnose isomerase from Escherichia coli and its relation with xylose isomerase illustrates a change between inter and intra-subunit complementation during evolution
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DOI：
10.1006/jmbi.2000.3896
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发表时间：
2000-07-21
影响因子：
5.6
通讯作者：
Matthews, BW
中科院分区：
文献类型：
--
作者：
Korndörfer, IP;Fessner, WD;Matthews, BW
利用一种新的表达构建体，从大肠杆菌中纯化和结晶鼠李糖异构酶。通过多次同晶置换解析晶体结构，并在1.6埃分辨率下细化至17.4%的晶体学残余。鼠李糖异构酶是四个（β/α）（8）-桶的紧密四聚体。与其他已知结构的比较表明，鼠李糖异构酶与木糖异构酶最相似。基于它们的结构的两种酶的序列的比对揭示了迄今未检测到的13%的序列同一性，这表明这两种酶从共同的前体进化而来。鼠李糖异构酶的（β/α）（8）-桶的结构和排列与木糖异构酶非常相似。然而，每种酶都有额外的α-螺旋结构域，这些结构域参与四聚体缔合，并且在结构上有很大差异。鼠李糖异构酶与抑制剂L-鼠李糖和天然底物L-鼠李糖的复合物的结构进行了测定，并表明，一个扩展的环，这是无序的天然酶，成为有序的底物结合，并可能排除散装溶剂在催化过程中。与木糖异构酶不同，该环不延伸穿过亚基界面，但有助于其自身亚基的活性位点。它说明了在进化过程中，亚基间和亚基内互补之间的相互转化是如何发生的。在晶体结构中（尽管不一定在体内），鼠李糖异构酶似乎在“结构”位点结合Zn 2+。在底物的存在下，该酶还在附近的“催化”位点结合Mn 2+。木糖异构酶中不存在的一系列疏水残基可能负责将L-鼠李糖识别为底物。现有的结构数据表明，金属介导的木糖异构酶，这通常是有利的，也是可行的鼠李糖异构酶的糖苷转移机制。(C)北京大学出版社.
Using a new expression construct, rhamnose isomerase from Escherichia coli was purified and crystallized. The crystal structure was solved by multiple isomorphous replacement and refined to a crystallographic residual of 17.4 % at 1.6 Angstrom resolution. Rhamnose isomerase is a tight tetramer of four (beta/alpha)(8)-barrels. A comparison with other known structures reveals that rhamnose isomerase is most similar to xylose isomerase. Alignment of the sequences of the two enzymes based on their structures reveals a hitherto undetected sequence identity of 13 %, suggesting that the two enzymes evolved from a common precursor. The structure and arrangement of the (beta/alpha)(8)-barrels of rhamnose isomerase are very similar to xylose isomerase. Each enzyme does, however, have additional a-helical domains, which are involved in tetramer association, and largely differ in structure. The structures of complexes of rhamnose isomerase with the inhibitor L-rhamnitol and the natural substrate L-rhamnose were determined and suggest that an extended loop, which is disordered in the native enzyme, becomes ordered on substrate binding, and may exclude bulk solvent during catalysis. Unlike xylose isomerase, this loop does not extend across a subunit interface but contributes to the active site of its own subunit. It illustrates how an interconversion between inter and intra-subunit complementation can occur during evolution. In the crystal structure (although not necessarily in vivo) rhamnose isomerase appears to bind Zn2+ at a "structural" site. In the presence of substrate the enzyme also binds Mn2+ at a nearby "catalytic" site. An array of hydrophobic residues, not present in xylose isomerase, is Likely to be responsible for the recognition of L-rhamnose as a substrate. The available structural data suggest that a metal-mediated hydride-shift mechanism, which is generally favored for xylose isomerase, is also feasible for rhamnose isomerase. (C) 2000 Academic Press.