Hoyle H D, Turner F R, Brunick L, Raff E C
Department of Biology and Indiana Molecular Biology Institute, Indiana University, Bloomington, Indiana 47405, USA.
Mol Biol Cell. 2001 Jul;12(7):2185-94. doi: 10.1091/mbc.12.7.2185.
We demonstrate sorting of beta-tubulins during dimerization in the Drosophila male germ line. Different beta-tubulin isoforms exhibit distinct affinities for alpha-tubulin during dimerization. Our data suggest that differences in dimerization properties are important in determining isoform-specific microtubule functions. The differential use of beta-tubulin during dimerization reveals structural parameters of the tubulin heterodimer not discernible in the resolved three-dimensional structure. We show that the variable beta-tubulin carboxyl terminus, a surface feature in the heterodimer and in microtubules, and which is disordered in the crystallographic structure, is of key importance in forming a stable alpha-beta heterodimer. If the availability of alpha-tubulin is limiting, alpha-beta dimers preferentially incorporate intact beta-tubulins rather than a beta-tubulin missing the carboxyl terminus (beta 2 Delta C). When alpha-tubulin is not limiting, beta 2 Delta C forms stable alpha-beta heterodimers. Once dimers are formed, no further sorting occurs during microtubule assembly: alpha-beta 2 Delta C dimers are incorporated into axonemes in proportion to their contribution to the total dimer pool. Co-incorporation of beta 2 Delta C and wild-type beta 2-tubulin results in nonmotile axonemes because of a disruption of the periodicity of nontubulin axonemal elements. Our data show that the beta-tubulin carboxyl terminus has two distinct roles: 1) forming the alpha-beta heterodimer, important for all microtubules and 2) providing contacts for nontubulin components required for specific microtubule structures, such as axonemes.
我们证明了在果蝇雄性生殖系二聚化过程中β-微管蛋白的分选。不同的β-微管蛋白亚型在二聚化过程中对α-微管蛋白表现出不同的亲和力。我们的数据表明，二聚化特性的差异对于确定亚型特异性微管功能很重要。二聚化过程中β-微管蛋白的差异使用揭示了在解析的三维结构中无法辨别的微管蛋白异二聚体的结构参数。我们表明，可变的β-微管蛋白羧基末端，是异二聚体和微管中的一个表面特征，在晶体结构中是无序的，对于形成稳定的α-β异二聚体至关重要。如果α-微管蛋白的可用性受到限制，α-β二聚体优先结合完整的β-微管蛋白，而不是缺少羧基末端的β-微管蛋白（β2ΔC）。当α-微管蛋白不受限制时，β2ΔC形成稳定的α-β异二聚体。一旦二聚体形成，在微管组装过程中就不会进一步分选：α-β2ΔC二聚体与其对总二聚体库的贡献成比例地并入轴丝。β2ΔC和野生型β2-微管蛋白的共同掺入导致轴丝无法运动，因为非微管蛋白轴丝元件的周期性被破坏。我们的数据表明，β-微管蛋白羧基末端有两个不同的作用：1）形成α-β异二聚体，这对所有微管都很重要；2）为特定微管结构（如轴丝）所需的非微管蛋白成分提供接触点。
