Coupled formation of an amidotransferase interdomain ammonia channel and a phosphoribosyltransferase active site
Coupled formation of an amidotransferase interdomain ammonia channel and a phosphoribosyltransferase active site
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DOI：
10.1021/bi9714114
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发表时间：
1997-09-16
期刊：
影响因子：
2.9
通讯作者：
Smith, JL
中科院分区：
文献类型：
--
作者：
Krahn, JM;Kim, JH;Smith, JL
通过与 PRPP 底物类似物结合激活谷氨酰胺磷酸核糖焦磷酸 (PRPP) 酰胺转移酶 (GPATase)，导致形成 20 埃通道，将一个结构域中的谷氨酰胺水解活性位点与第二个结构域中的 PRPP 位点连接起来。这种溶剂无法进入的通道允许 NH3 中间体在两个活性位点之间转移。 NH3 的隧道效应可能是谷氨酰胺酰胺转移酶催化的氮转移以及复合酶中两个不同活性位点催化协调的常见机制。 GPATase 活性构象异构体的 2.4 埃晶体结构还首次描述了核苷酸合成和补救酶的磷酸核糖基转移酶 (PRTase) 家族的完整活性位点。在所提出的基于结构的机制中，化学辅助催化主要由底物提供，其次由酶提供。二价阳离子与 PRTase 活性位点结合的不同催化和抑制模式在酶的活性构象异构体和反馈抑制的 GMP 复合物中揭示。
Activation of glutamine phosphoribosylpyrophosphate (PRPP) amidotransferase (GPATase) by binding of a PRPP substrate analog results in the formation of a 20 Angstrom channel connecting the active site for glutamine hydrolysis in one domain with the PRPP site in a second domain. This solvent-inaccessible channel permits transfer of the NH3 intermediate between the two active sites. Tunneling of NH3 may be a common mechanism for glutamine amidotransferase-catalyzed nitrogen transfer and for coordination of catalysis at two distinct active sites in complex enzymes. The 2.4 Angstrom crystal structure of the active conformer of GPATase also provides the first description of an intact active site for the phosphoribosyltransferase (PRTase) family of nucleotide synthesis and salvage enzymes. Chemical assistance to catalysis is provided primarily by the substrate and secondarily by the enzyme in the proposed structure-based mechanism. Different catalytic and inhibitory modes of divalent cation binding to the PRTase active site are revealed in the active conformer of the enzyme and in a feedback-inhibited GMP complex.