Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN.
Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN.
J Cell Biol. 2021 Oct 4;220(10). doi: 10.1083/jcb.202012144. Epub 2021 Jul 29.
The GTP-tubulin cap is widely accepted to protect microtubules against catastrophe. The GTP-cap size is thought to increase with the microtubule growth rate, presumably endowing fast-growing microtubules with enhanced stability. It is unknown what GTP-cap properties permit frequent microtubule catastrophe despite fast growth. Here, we investigate microtubules growing in the presence and absence of the polymerase XMAP215. Using EB1 as a GTP-cap marker, we find that GTP-cap size increases regardless of whether growth acceleration is achieved by increasing tubulin concentration or by XMAP215. Despite increased mean GTP-cap size, microtubules grown with XMAP215 display increased catastrophe frequency, in contrast to microtubules grown with more tubulin, for which catastrophe is abolished. However, microtubules polymerized with XMAP215 have large fluctuations in growth rate; display tapered and curled ends; and undergo catastrophe at faster growth rates and with higher EB1 end-localization. Our results suggest that structural perturbations induced by XMAP215 override the protective effects of the GTP-cap, ultimately driving microtubule catastrophe.
GTP-微管蛋白帽被广泛认为可以保护微管免受解体。微管生长速度越快，GTP 帽的大小就越大，这可能使快速生长的微管具有更强的稳定性。目前尚不清楚是什么 GTP 帽特性使得微管在快速生长的同时频繁发生解体。在这里，我们研究了在有和没有聚合酶 XMAP215 的情况下生长的微管。我们使用 EB1 作为 GTP-帽标记，发现无论通过增加微管蛋白浓度还是通过 XMAP215 来加速生长，GTP-帽的大小都会增加。尽管平均 GTP-帽的大小增加了，但与用更多微管蛋白生长的微管相比，用 XMAP215 生长的微管显示出更高的解体频率，而用更多微管蛋白生长的微管则消除了解体。然而，用 XMAP215 聚合的微管的生长速率波动很大；显示出锥形和卷曲的末端；并且在更高的 EB1 末端定位和更快的生长速率下发生解体。我们的结果表明，XMAP215 诱导的结构扰动超过了 GTP 帽的保护作用，最终导致微管解体。
