Transition state analogues in structures of ricin and saporin ribosome-inactivating proteins
Transition state analogues in structures of ricin and saporin ribosome-inactivating proteins
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DOI：
10.1073/pnas.0911606106
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发表时间：
2009-12-01
影响因子：
11.1
通讯作者：
Schramm, Vern L.
中科院分区：
文献类型：
--
作者：
Ho, Meng-Chiao;Sturm, Matthew B.;Schramm, Vern L.
Ricin A-chain （RTA）和saporin-L1 （SAP）催化28S rRNA的腺苷去嘌呤，抑制蛋白合成，导致细胞死亡。我们研究了与过渡态类似物抑制剂配合的RTA和SAP的晶体结构。这些紧密结合抑制剂模拟28S rRNA的肌毒素-蓖麻毒素识别环和为RTA催化建立的解离核糖化过渡态。RTA和SAP具有独特的嘌呤结合几何结构，邻近的腺嘌呤和鸟嘌呤碱基与2个保守的酪氨酸之间存在四倍pi堆叠相互作用。在pi-stack一端的精氨酸为敏感腺嘌呤提供阳离子极化和增强的离去基能力。这些核糖体失活蛋白的共同特征包括腺嘌呤离开基团活化，明显缺乏核位稳定性，以及作为H2O亲核试剂活化的一般碱基的保守谷氨酸。催化力主要来自与过渡态类似物的RTA和SAP复合物中明显的离去基活化。
Ricin A-chain (RTA) and saporin-L1 (SAP) catalyze adenosine depurination of 28S rRNA to inhibit protein synthesis and cause cell death. We present the crystal structures of RTA and SAP in complex with transition state analogue inhibitors. These tight-binding inhibitors mimic the sarcin-ricin recognition loop of 28S rRNA and the dissociative ribocation transition state established for RTA catalysis. RTA and SAP share unique purine-binding geometry with quadruple pi-stacking interactions between adjacent adenine and guanine bases and 2 conserved tyrosines. An arginine at one end of the pi-stack provides cationic polarization and enhanced leaving group ability to the susceptible adenine. Common features of these ribosome-inactivating proteins include adenine leaving group activation, a remarkable lack of ribocation stabilization, and conserved glutamates as general bases for activation of the H2O nucleophile. Catalytic forces originate primarily from leaving group activation evident in both RTA and SAP in complex with transition state analogues.