Readout of the tubulin code by cellular effectors

微管是细胞形态发生、细胞分裂和细胞内运输所必需的聚合物。它们受到高度多样化、丰富和进化保守的翻译后修饰。微管蛋白修饰水平和模式的破坏导致癌症、神经病变和轴突再生缺陷。我们的长期目标是了解细胞如何利用微管蛋白异构体多样性和翻译后修饰来调节微管的结构和动力学，以及它们与分子马达和微管相关蛋白（MAPs）的相互作用。尽管在三十多年前就发现了微管蛋白，但对其化学和遗传复杂性的作用的理解仍然难以捉摸。我的团队整合了生物物理学、蛋白质组学、结构和细胞生物学的技术和概念，以解决微管细胞生物学中的这一基本问题。

Microtubules are polymers essential for cell morphogenesis, cell division and intracellular transport. They are subject to highly diverse, abundant and evolutionarily conserved post-translational modifications. Disruption of tubulin modification levels and patterns leads to cancers, neuropathologies and defective axonal regeneration. Our long-term goal is to understand how cells use tubulin isoform diversity and posttranslational modifications to regulate the structure and dynamics of microtubules as well as their interactions with molecular motors and microtubule associated proteins (MAPs). Although discovered over thirty years ago, an understanding of the roles of the chemical and genetic complexity of tubulin has remained elusive. My group integrates techniques and concepts from biophysics, proteomics, structural and cell biology to address this fundamental problem in microtubule cell biology. My laboratory has made significant progress towards these goals. These include: (1) development of novel methods for generating homogenous engineered single isoform recombinant unmodified human tubulin (Vemu et al., J. Biol. Chem., 2016); (2) determination of the first structure and dynamic instability parameters of recombinant isotopically pure recombinant neuronal tubulin (Vemu et al., J. Biol. Chem., 2016); (3) development of a biochemical platform for obtaining tubulin with quantitatively defined levels of posttranslational modifications (Valenstein and Roll-Mecak, Cell 2016) and use of this platform to (4) show the graded response of an important microtubule regulator, the hereditary spastic paraplegia protein spastin, to tubulin glutamylation (Valenstein and Roll-Mecak, Cell 2016) thus furnishing strong support for the tubulin code hypothesis. Our most recent work shows that microtubules with different isoform compositions exhibit dramatically different dynamic properties and that these properties can be proportionally tuned by varying tubulin isoform composition (Vemu et al., Mol. Biol. Cell, 2017). This indicates that the changes in isoform expression observed during morphogenesis and tumorigensis have a direct impact on microtubule dynamics and do not need to be mediated in trans through effectors. Using our platform for generating quantitatively defined modified microtubules as well recombinant engineered human microtubules, we will continue to interrogate how the tubulin code, both through genetic variation and posttranslational modifications, regulates the basic biophysical properties of microtubules as well as molecular motors and neuronal MAPs with strong involvement in neurodegenerative disorders.