Ricin A-Chain Inhibitors Resembling the Oxacarbenium Ion Transition State
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- 作者：Kelly S. E. Tanaka ; Xiang-Yang Chen ; Yoshitaka Ichikawa ; Peter C. Tyler ; Richard H. Furneaux ; and Vern L. Schramm
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：June 12, 2001
- 年：2001
- 卷：40
- 期：23
- 页码：6845 - 6851
- 全文大小：84K
- 年卷期：v.40,no.23(June 12, 2001)
- ISSN：1520-4995
文摘
Ricin toxin A-chain (RTA) is expressed by the castor bean plant and is among the most potentmammalian toxins. Upon activation in the cytosol, RTA depurinates a single adenine from position 4324of rat 28S ribosomal RNA, causing inactivation of ribosomes by preventing the binding of elongationfactors. Kinetic isotope effect studies have established that RTA operates via a DN*AN mechanism involvingan oxacarbenium ion intermediate with bound adenine [Chen, X.-Y., Berti, P. J., and Schramm, V. L.(2000) J. Am. Chem. Soc. 122, 1609-1617]. On the basis of this information, stem-loop RNA moleculeswere chemically synthesized, incorporating structural features of the oxacarbenium ion-like transitionstate. A 10-base RNA stem-loop incorporating (1S)-1-(9-deazaadenin-9-yl)-1,4-dideoxy-1,4-imino-D-ribitol at the depurination site binds four times better (0.57 
M) than the 10-base RNA stem-loop withadenosine at the depurination site (2.2 M). A 10-base RNA stem-loop with 1,2-dideoxyribitol [(2R,3S)-2-(hydroxymethyl)-3-hydroxytetrahydrofuran] at the depurination site binds with a Kd of 3.2 M andtightens to 0.75 M in the presence of 9-deazaadenine. A similar RNA stem-loop with 1,4-dideoxy-1,4-imino-D-ribitol at the depurination site binds with a Kd of 1.3 M and improves to 0.65 M with9-deazaadenine added. When (3S,4R)-4-hydroxy-3-(hydroxymethyl)pyrrolidine was incorporated at thedepurination site of a 14-base RNA stem-loop, the Kd was 0.48 M. Addition of 9-deazaadenine tightensthe binding to 0.10 M whereas added adenine increases the affinity to 12 nM. The results of this studyare consistent with the unusual dissociative DN*AN mechanism determined for RTA. Knowledge of thisintermediate has led to the design and synthesis of the highest affinity inhibitor reported for the catalyticsite of RTA.
M) than the 10-base RNA stem-loop withadenosine at the depurination site (2.2 M). A 10-base RNA stem-loop with 1,2-dideoxyribitol [(2R,3S)-2-(hydroxymethyl)-3-hydroxytetrahydrofuran] at the depurination site binds with a Kd of 3.2 M andtightens to 0.75 M in the presence of 9-deazaadenine. A similar RNA stem-loop with 1,4-dideoxy-1,4-imino-D-ribitol at the depurination site binds with a Kd of 1.3 M and improves to 0.65 M with9-deazaadenine added. When (3S,4R)-4-hydroxy-3-(hydroxymethyl)pyrrolidine was incorporated at thedepurination site of a 14-base RNA stem-loop, the Kd was 0.48 M. Addition of 9-deazaadenine tightensthe binding to 0.10 M whereas added adenine increases the affinity to 12 nM. The results of this studyare consistent with the unusual dissociative DN*AN mechanism determined for RTA. Knowledge of thisintermediate has led to the design and synthesis of the highest affinity inhibitor reported for the catalyticsite of RTA.