Larsen Nicholas A, Harrison Stephen C
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
J Mol Biol. 2004 Dec 3;344(4):885-92. doi: 10.1016/j.jmb.2004.09.094.
Bub3 is one of at least six proteins that transmit the spindle assembly checkpoint signal. These proteins delay cell cycle progression from metaphase to anaphase in response to attachment defects between kinetochores and spindle microtubules and to tension defects between sister chromatids. To explore the molecular interactions mediated by Bub3, we have determined the crystal structure of the Saccharomyces cerevisiae protein Bub3p at 2.35 A resolution. Bub3p is a seven-blade beta-propeller, although its sequence diverges from that of other WD40 family members. Several loops are substantially elongated, but extra domains or insertions are not present at the termini. In particular, two extended loops project from the top face of the propeller, forming a cleft. Amino acid residues across the top face and one aspect of the lateral surface (spanning blades 5-6) are highly conserved among Bub3 proteins. We propose that these conserved surfaces are the loci for key interactions with conserved motifs in spindle checkpoint proteins Bub1 and Mad3/BubR1. Comparison of the Bub3 sequence to the WD40 protein, Rae1, shows high sequence conservation along the same surfaces. Rae1 interaction with Bub1 is, therefore, likely to involve a similar mode of binding.
Bub3是至少六种传递纺锤体组装检查点信号的蛋白质之一。这些蛋白质会响应动粒与纺锤体微管之间的附着缺陷以及姐妹染色单体之间的张力缺陷，延迟细胞周期从中期到后期的进程。为了探究由Bub3介导的分子相互作用，我们已确定酿酒酵母蛋白质Bub3p的晶体结构，分辨率为2.35埃。Bub3p是一个七叶β-螺旋桨，尽管其序列与其他WD40家族成员的序列不同。有几个环显著延长，但在末端没有额外的结构域或插入序列。特别是，有两个延伸的环从螺旋桨的顶面伸出，形成一个裂缝。在Bub3蛋白质中，螺旋桨顶面和侧面一个面（跨越叶片5-6）上的氨基酸残基高度保守。我们提出，这些保守表面是与纺锤体检查点蛋白质Bub1和Mad3/BubR1中的保守基序进行关键相互作用的位点。将Bub3序列与WD40蛋白质Rae1进行比较，发现在相同表面上具有高度的序列保守性。因此，Rae1与Bub1的相互作用可能涉及类似的结合模式。
