Chaaban Sami, Brouhard Gary J
Department of Biology, McGill University, Montreal, QC H3A 1B1, Canada.
Department of Biology, McGill University, Montreal, QC H3A 1B1, Canada
Mol Biol Cell. 2017 Nov 1;28(22):2924-2931. doi: 10.1091/mbc.E16-05-0271.
Microtubules are long, slender polymers of αβ-tubulin found in all eukaryotic cells. Tubulins associate longitudinally to form protofilaments, and adjacent protofilaments associate laterally to form the microtubule. In the textbook view, microtubules are 1) composed of 13 protofilaments, 2) arranged in a radial array by the centrosome, and 3) built into the 9+2 axoneme. Although these canonical structures predominate in eukaryotes, microtubules with divergent protofilament numbers and higher-order microtubule assemblies have been discovered throughout the last century. Here we survey these noncanonical structures, from the 4-protofilament microtubules of to the 40-protofilament accessory microtubules of mantidfly sperm. We review the variety of protofilament numbers observed in different species, in different cells within the same species, and in different stages within the same cell. We describe the determinants of protofilament number, namely nucleation factors, tubulin isoforms, and posttranslational modifications. Finally, we speculate on the functional significance of these diverse polymers. Equipped with novel tubulin-purification tools, the field is now prepared to tackle the long-standing question of the evolutionary basis of microtubule structure.
微管是存在于所有真核细胞中的由αβ-微管蛋白构成的长而细的聚合物。微管蛋白纵向结合形成原丝，相邻原丝横向结合形成微管。按照教科书的观点，微管具有以下特点：1）由13条原丝组成；2）由中心体呈放射状排列；3）构建成9+2轴丝。尽管这些典型结构在真核生物中占主导地位，但在过去的一个世纪里，已经发现了原丝数量不同和具有更高阶微管组装的微管。在这里，我们将审视这些非典型结构，从[具体生物]的4条原丝微管到螳蛉精子的40条原丝辅助微管。我们回顾了在不同物种、同一物种的不同细胞以及同一细胞的不同阶段观察到的原丝数量的多样性。我们描述了原丝数量的决定因素，即成核因子、微管蛋白亚型和翻译后修饰。最后，我们推测这些不同聚合物的功能意义。有了新型的微管蛋白纯化工具，该领域现在准备好解决微管结构进化基础这个长期存在的问题。
