Dissecting Paclitaxel鈥揗icrotubule Association: Quantitative Assessment of the 2鈥?OH Group
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- 作者：Shubhada Sharma ; Chandraiah Lagisetti ; Barbara Poliks ; Robert M. Coates ; David G. I. Kingston ; Susan Bane
- 刊名：Biochemistry
- 出版年：2013
- 出版时间：April 2, 2013
- 年：2013
- 卷：52
- 期：13
- 页码：2328-2336
- 全文大小：363K
- 年卷期：v.52,no.13(April 2, 2013)
- ISSN：1520-4995
文摘
Paclitaxel (PTX) is a microtubule-stabilizing agent that is widely used in cancer chemotherapy. This structurally complex natural product acts by binding to 尾-tubulin in assembled microtubules. The 2鈥?hydroxyl group in the flexible side chain of PTX is an absolute requirement for activity, but its precise role in the drug鈥搑eceptor interaction has not been specifically investigated. The contribution of the 2鈥?OH group to the affinity and tubulin-assembly efficacy of PTX has been evaluated through quantitative analysis of PTX derivatives possessing side chain deletions: 2鈥?deoxy-PTX, N-debenzoyl-2鈥?deoxy-PTX, and baccatin III. The affinity of 2鈥?deoxy-PTX for stabilized microtubules was more than 100-fold lower than that of PTX and only 3-fold greater than the microtubule affinity of baccatin III. No microtubule binding activity was detected for the analogue N-debenzoyl-2鈥?deoxy-PTX. The tubulin-assembly efficacy of each ligand was consistent with the microtubule binding affinity, as was the trend in cytotoxicities. Molecular dynamics simulations revealed that the 2鈥?OH group of PTX can form a persistent hydrogen bond with D26 within the microtubule binding site. The absence of this interaction between 2鈥?deoxy-PTX and the receptor can account for the difference in binding free energy. Computational analyses also provide a possible explanation for why N-debenzoyl-2鈥?deoxy-PTX is inactive, in spite of the fact that it is essentially a substituted baccatin III. We propose that the hydrogen bonding interaction between the 2鈥?OH group and D26 is the most important stabilizing interaction that PTX forms with tubulin in the region of the C-13 side chain. We further hypothesize that the substituents at the 3鈥?position function to orient the 2鈥?OH group for a productive hydrogen bonding interaction with the protein.