A microtubule-associated protein from Xenopus eggs that specifically promotes assembly at the plus-end.
A microtubule-associated protein from Xenopus eggs that specifically promotes assembly at the plus-end.
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DOI：
10.1083/jcb.105.5.2203
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发表时间：
1987-11
期刊：
影响因子：
--
通讯作者：
Kirschner MW
中科院分区：
文献类型：
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作者：
Gard DL;Kirschner MW
我们已经从爪蟾卵中分离出一种促进体外微管组装的蛋白质因子。在活性富集1000 - 3000倍后，组装促进与215-kD蛋白相关。这个215- kD的蛋白被称为爪蟾微管组装蛋白（Xenopus microtule assembly protein， XMAP），与微管结合的化学计量为0.06 mol/mol微管蛋白二聚体。XMAP在免疫学上不同于爪蟾与哺乳动物脑微管相关蛋白的同源物；然而，在爪蟾的神经组织和睾丸中发现了与XMAP有不同分子质量的免疫相关蛋白。XMAP是不寻常的，因为它特别促进微管在正端的组装。在0.01 mol XMAP/mol微管的摩尔比下，微管正端组装速率加快了8倍，而负端组装速率仅提高了1.8倍。在这些条件下，XMAP使on-rate常数增加了10倍（从1.4 s到1）。从纯微管蛋白到15s -1组装的微管。μ m -1)，速率常数降低10倍（从340 s-1降至34 s-1）。鉴于其体内的化学计量，XMAP一定是爪蟾卵中主要的微管组装因子。XMAP在减数分裂周期和有丝分裂周期的m期都被磷酸化，这表明它的活性可能在细胞周期中受到调节。
We have isolated a protein factor from Xenopus eggs that promotes microtubule assembly in vitro. Assembly promotion was associated with a 215-kD protein after a 1,000-3,000-fold enrichment of activity. The 215- kD protein, termed Xenopus microtubule assembly protein (XMAP), binds to microtubules with a stoichiometry of 0.06 mol/mol tubulin dimer. XMAP is immunologically distinct from the Xenopus homologues to mammalian brain microtubule-associated proteins; however, protein species immunologically related to XMAP with different molecular masses are found in Xenopus neuronal tissues and testis. XMAP is unusual in that it specifically promotes microtubule assembly at the plus-end. At a molar ratio of 0.01 mol XMAP/mol tubulin the assembly rate of the microtubule plus-end is accelerated 8-fold while the assembly rate of the minus-end is increased only 1.8-fold. Under these conditions XMAP promotes a 10-fold increase in the on-rate constant (from 1.4 s- 1.microM-1 for microtubules assembled from pure tubulin to 15 s- 1.microM-1), and a 10-fold decrease in off-rate constant (from 340 to 34 s-1). Given its stoichiometry in vivo, XMAP must be the major microtubule assembly factor in the Xenopus egg. XMAP is phosphorylated during M-phase of both meiotic and mitotic cycles, suggesting that its activity may be regulated during the cell cycle.