Three-dimensional topology of the SMC2/SMC4 subcomplex from chicken condensin I revealed by cross-linking and molecular modelling
Three-dimensional topology of the SMC2/SMC4 subcomplex from chicken condensin I revealed by cross-linking and molecular modelling
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DOI：
10.1098/rsob.150005
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发表时间：
2015-02-01
期刊：
影响因子：
5.8
通讯作者：
Earnshaw, William C.
中科院分区：
文献类型：
--
作者：
Barysz, Helena;Kim, Ji Hun;Earnshaw, William C.
SMC蛋白是三种蛋白复合物的基本组成部分，对染色体的结构和功能至关重要。凝聚素复合体将复制的姐妹染色单体保持在一起，而凝聚素复合体在有丝分裂染色体结构中起重要作用。两者都参与间期基因组的组织。含SMC的复合物很大（对于凝聚素大于650 kDa），并且含有长的反平行卷曲螺旋。因此，它们是传统晶体学和电子低温显微镜研究的困难课题。在这里，我们已经使用氨基酸选择性交联和质谱结合结构预测，以开发一个全长的分子草案的三维结构的SMC 2/SMC 4二聚体骨架的鸡凝聚素。我们组装了基于同源性的球状头部和铰链的分子模型，其中冗长的卷曲螺旋以片段为模型，使用许多高置信度的交联并考虑潜在的不规则性。我们的实验表明，孤立的凝聚复合物可以存在与他们的卷曲螺旋段紧密并列彼此沿着他们的长度和定义的两个反平行线圈的相对空间排列。在有丝分裂染色体中，卷曲螺旋的中心也可以在原位相互接近。除了揭示结构信息，我们的交联数据表明，H2 A和H4都可能在凝聚素与染色质的相互作用中发挥作用。
SMC proteins are essential components of three protein complexes that are important for chromosome structure and function. The cohesin complex holds replicated sister chromatids together, whereas the condensin complex has an essential role in mitotic chromosome architecture. Both are involved in interphase genome organization. SMC-containing complexes are large (more than 650 kDa for condensin) and contain long anti-parallel coiled-coils. They are thus difficult subjects for conventional crystallographic and electron cryomicroscopic studies. Here, we have used amino acid-selective cross-linking and mass spectrometry combined with structure prediction to develop a full-length molecular draft three-dimensional structure of the SMC2/SMC4 dimeric backbone of chicken condensin. We assembled homology-based molecular models of the globular heads and hinges with the lengthy coiled-coils modelled in fragments, using numerous high-confidence cross-links and accounting for potential irregularities. Our experiments reveal that isolated condensin complexes can exist with their coiled-coil segments closely apposed to one another along their lengths and define the relative spatial alignment of the two anti-parallel coils. The centres of the coiled-coils can also approach one another closely in situ in mitotic chromosomes. In addition to revealing structural information, our cross-linking data suggest that both H2A and H4 may have roles in condensin interactions with chromatin.