Nucleotide complexes of Escherichia coli phosphoribosylaminoimidazole succinocarboxamide synthetase
Nucleotide complexes of Escherichia coli phosphoribosylaminoimidazole succinocarboxamide synthetase
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DOI：
10.1074/jbc.m602109200
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发表时间：
2006-07-28
影响因子：
4.8
通讯作者：
Honzatko, Richard B.
中科院分区：
文献类型：
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作者：
Ginder, Nathaniel D.;Binkowski, Daniel J.;Honzatko, Richard B.
Phosphoribosylaminoimidazole-succinocarboxamide合成酶(SAICAR合成酶)将4-羧基-5-氨基咪唑核苷酸(CAIR)转化为4-(N-琥珀酰基甲酰胺)-5-氨基咪唑(SAICAR)核苷酸。这种酶是损害细胞生长的天然产物的靶标。本文报道了ADP和ADP()的晶体结构。大肠杆菌SAICAR合成酶的CAIR复合体，后者是CAIR连接的SAICAR合成酶的第一个实例。ADP和CAIR与活性中心结合，与三个镁离子结合，其中两个与CAIR的4-羧基配位相同的氧原子，第三个与ADP的α-和β-磷酰基配位。ADP(.)CAIR络合物是磷酰化转移反应过渡态模型的基础，也支持另一种化学途径，即L-天冬氨酸的亲核攻击先于磷酰化转移反应。大肠杆菌结构中204-221位残基的多肽折叠与来自Thermatoga maritima的无配体SAICAR合成酶和来自酿酒酵母的合成酶的腺嘌呤核苷酸复合体显著不同。大肠杆菌、毛滴虫和酵母合成酶之间的构象差异表明，在微生物中选择性地抑制从头开始的嘌呤核苷酸生物合成的可能性。
Phosphoribosylaminoimidazole-succinocarboxamide synthetase ( SAICAR synthetase) converts 4-carboxy-5-aminoimidazole ribonucleotide ( CAIR) to 4-( N-succinylcarboxamide)-5-aminoimidazole ribonucleotide ( SAICAR). The enzyme is a target of natural products that impair cell growth. Reported here are the crystal structures of the ADP and the ADP (.) CAIR complexes of SAICAR synthetase from Escherichia coli, the latter being the first instance of a CAIR-ligated SAICAR synthetase. ADP and CAIR bind to the active site in association with three Mg2+, two of which coordinate the same oxygen atom of the 4- carboxyl group of CAIR; whereas, the third coordinates the alpha- and beta-phosphoryl groups of ADP. The ADP (.) CAIR complex is the basis for a transition state model of a phosphoryl transfer reaction involving CAIR and ATP, but also supports an alternative chemical pathway in which the nucleophilic attack of L-aspartate precedes the phosphoryl transfer reaction. The polypeptide fold for residues 204 - 221 of the E. coli structure differs significantly from those of the ligand-free SAICAR synthetase from Thermatoga maritima and the adenine nucleotide complexes of the synthetase from Saccharomyces cerevisiae. Conformational differences between the E. coli, T. maritima, and yeast synthetases suggest the possibility of selective inhibition of de novo purine nucleotide biosynthesis in microbial organisms.