Department of Experimental Oncology, European Institute of Oncology, 20139 Milan, Italy.
J Cell Biol. 2012 Feb 20;196(4):451-67. doi: 10.1083/jcb.201110013. Epub 2012 Feb 13.
The function of the essential checkpoint kinases Bub1 and BubR1 requires their recruitment to mitotic kinetochores. Kinetochore recruitment of Bub1 and BubR1 is proposed to rely on the interaction of the tetratricopeptide repeats (TPRs) of Bub1 and BubR1 with two KI motifs in the outer kinetochore protein Knl1. We determined the crystal structure of the Bub1 TPRs in complex with the cognate Knl1 KI motif and compared it with the structure of the equivalent BubR1TPR-KI motif complex. The interaction developed along the convex surface of the TPR assembly. Point mutations on this surface impaired the interaction of Bub1 and BubR1 with Knl1 in vitro and in vivo but did not cause significant displacement of Bub1 and BubR1 from kinetochores. Conversely, a 62-residue segment of Bub1 that includes a binding domain for the checkpoint protein Bub3 and is C terminal to the TPRs was necessary and largely sufficient for kinetochore recruitment of Bub1. These results shed light on the determinants of kinetochore recruitment of Bub1.
必需检查点激酶 Bub1 和 BubR1 的功能需要它们被招募到有丝分裂的动粒上。Bub1 和 BubR1 向动粒的募集被认为依赖于 Bub1 和 BubR1 的四肽重复（TPR）与外动粒蛋白 Knl1 中的两个 KI 基序的相互作用。我们确定了与同源 Knl1 KI 基序复合物的 Bub1 TPR 的晶体结构，并将其与等效的 BubR1TPR-KI 基序复合物的结构进行了比较。该相互作用沿着 TPR 组装体的凸面发展。该表面上的点突变会在体外和体内损害 Bub1 和 BubR1 与 Knl1 的相互作用，但不会导致 Bub1 和 BubR1 从动粒上显著位移。相反，Bub1 的 62 个残基片段包含与检查点蛋白 Bub3 的结合域，并且位于 TPR 的 C 末端，对于 Bub1 的动粒募集是必需的并且在很大程度上是足够的。这些结果阐明了 Bub1 向动粒募集的决定因素。
