Structural elements in IGP synthase exclude water to optimize ammonia transfer
Structural elements in IGP synthase exclude water to optimize ammonia transfer
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DOI：
10.1529/biophysj.104.058651
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发表时间：
2005-07-01
影响因子：
3.4
通讯作者：
Luthey-Schulten, ZA
中科院分区：
文献类型：
--
作者：
Amaro, RE;Myers, RS;Luthey-Schulten, ZA
在组氨酸生物合成的复杂途径中，连接氨基酸和嘌呤生物合成的关键分支点是由双功能酶咪唑甘油磷酸(IGP)合成酶催化的。IGP合成酶的第一个结构域是三联体谷氨酰胺转氨酶，它能水解谷氨酰胺生成谷氨酸和氨。它的活性受到底物PrFAR与其伙伴合酶结构域的结合的严格调控。最近的晶体结构和分子动力学模拟有力地表明，合成酶结构域是一个(β/α)(8)桶蛋白，通过将氨从一个远程活性部位引导到另一个活性部位，在IGP中介导氨的插入和环的形成。在这里，我们结合诱变实验和计算研究来深入了解氨的转移和传导机制。我们发现了氨进入(β/α)(8)桶的另一种途径，并认为水既是酶功能的激动剂，也是酶功能的拮抗剂。我们的结果表明，这两个亚域的结构，最值得注意的是，在界面和(β/α)(8)桶内的关键残基的严格保守，已经被优化，以允许氨而不是水在两个远程活性中心之间有效地通过。
In the complex pathway of histidine biosynthesis, a key branch point linking amino acid and purine biosynthesis is catalyzed by the bifunctional enzyme imidazole glycerol phosphate (IGP) synthase. The first domain of IGP synthase, a triad glutamine amidotransferase, hydrolyzes glutamine to form glutamate and ammonia. Its activity is tightly regulated by the binding of the substrate PRFAR to its partner synthase domain. Recent crystal structures and molecular dynamics simulations strongly suggest that the synthase domain, a (beta/alpha)(8) barrel protein, mediates the insertion of ammonia and ring formation in IGP by channeling ammonia from one remote active site to the other. Here, we combine both mutagenesis experiments and computational investigations to gain insight into the transfer of ammonia and the mechanism of conduction. We discover an alternate route for the entrance of ammonia into the (beta/alpha)(8) barrel and argue that water acts as both agonist and antagonist to the enzymatic function. Our results indicate that the architecture of the two subdomains, most notably the strict conservation of key residues at the interface and within the (beta/alpha)(8) barrel, has been optimized to allow the efficient passage of ammonia, and not water, between the two remote active sites.