Ross Jennifer L, Santangelo Christian D, Makrides Victoria, Fygenson D Kuchnir
Department of Physics, University of California, Santa Barbara, CA 93106, USA.
Proc Natl Acad Sci U S A. 2004 Aug 31;101(35):12910-5. doi: 10.1073/pnas.0402928101. Epub 2004 Aug 23.
Taxol and tau are two ligands that stabilize the microtubule (MT) lattice. Taxol is an anti-mitotic drug that binds beta tubulin in the MT interior. Tau is a MT-associated protein that binds both alpha and beta tubulin on the MT exterior. Both Taxol and tau reduce MT dynamics and promote tubulin polymerization. Tau alone also acts to bundle, stiffen, and space MTs. A structural study recently suggested that Taxol and tau may interact by binding to the same site. Using fluorescence recovery after photobleaching, we find that tau induces Taxol to bind MTs cooperatively depending on the tau concentration. We develop a model that correctly fits the data in the absence of tau, yields the equilibrium dissociation constant of approximately 2 microM, and determines the escape rate of Taxol through one pore to be 1.7 x 10(3) (M x s)(-1). Extension of the model yields a measure of Taxol cooperativity with a Hill coefficient of at least 15 when tau is present at a 1:1 molar ratio with tubulin.
紫杉醇和微管相关蛋白tau是两种能够稳定微管（MT）晶格的配体。紫杉醇是一种抗有丝分裂药物，它结合在微管内部的β微管蛋白上。tau是一种微管相关蛋白，它在微管外部同时结合α和β微管蛋白。紫杉醇和tau都能降低微管动力学并促进微管蛋白聚合。单独的tau也具有使微管成束、变硬和分隔微管的作用。最近的一项结构研究表明，紫杉醇和tau可能通过结合到同一位点相互作用。利用光漂白后的荧光恢复技术，我们发现tau会诱导紫杉醇根据tau浓度协同结合微管。我们开发了一个模型，该模型在没有tau的情况下能正确拟合数据，得出约2微摩尔的平衡解离常数，并确定紫杉醇通过一个孔的逃逸速率为1.7×10³（摩尔×秒）⁻¹。当tau与微管蛋白以1:1摩尔比存在时，该模型的扩展得出紫杉醇协同性的一个量度，其希尔系数至少为15。
