Bioinformatics Institute, A(∗)STAR, Singapore 138671, Singapore; Friedrich Miescher Laboratory of the Max Planck Society, Tuebingen 72076, Germany.
Bioinformatics Institute, A(∗)STAR, Singapore 138671, Singapore.
Mol Cell. 2016 Sep 15;63(6):1044-54. doi: 10.1016/j.molcel.2016.08.008. Epub 2016 Sep 8.
Cohesin is a ring-shaped protein complex that is capable of embracing DNA. Most of the ring circumference is comprised of the anti-parallel intramolecular coiled coils of the Smc1 and Smc3 proteins, which connect globular head and hinge domains. Smc coiled coil arms contain multiple acetylated and ubiquitylated lysines. To investigate the role of these modifications, we substituted lysines for arginines to mimic the unmodified state and uncovered genetic interaction between the Smc arms. Using scanning force microscopy, we show that wild-type Smc arms associate with each other when the complex is not on DNA. Deacetylation of the Smc1/Smc3 dimers promotes arms' dissociation. Smc arginine mutants display loose packing of the Smc arms and, although they dimerize at the hinges, fail to connect the heads and associate with the DNA. Our findings highlight the importance of a "collapsed ring," or "rod," conformation of cohesin for its loading on the chromosomes.
黏合蛋白是一种能够环抱 DNA 的环形蛋白复合物。该环的大部分圆周由 Smc1 和 Smc3 蛋白的反平行分子内螺旋线圈组成，这些蛋白连接着球状头部和铰链结构域。Smc 螺旋线圈的臂含有多个乙酰化和泛素化的赖氨酸。为了研究这些修饰的作用，我们用精氨酸取代赖氨酸来模拟未修饰的状态，并发现 Smc 臂之间存在遗传相互作用。通过扫描力显微镜，我们发现当复合物不在 DNA 上时，野生型 Smc 臂会相互结合。Smc1/Smc3 二聚体的去乙酰化会促进臂的解离。Smc 精氨酸突变体显示 Smc 臂的松散包装，尽管它们在铰链处二聚化，但无法连接头部并与 DNA 结合。我们的研究结果强调了黏合蛋白的“折叠环”或“杆”构象对于其在染色体上的加载的重要性。
