Waldman Vincent M, Stanage Tyler H, Mims Alexandra, Norden Ian S, Oakley Martha G
Department of Chemistry, Indiana University, Bloomington, Indiana, 47405.
Proteins. 2015 Jun;83(6):1027-45. doi: 10.1002/prot.24778. Epub 2015 Apr 7.
The structural maintenance of chromosomes (SMC) proteins form the cores of multisubunit complexes that are required for the segregation and global organization of chromosomes in all domains of life. These proteins share a common domain structure in which N- and C- terminal regions pack against one another to form a globular ATPase domain. This "head" domain is connected to a central, globular, "hinge" or dimerization domain by a long, antiparallel coiled coil. To date, most efforts for structural characterization of SMC proteins have focused on the globular domains. Recently, however, we developed a method to map interstrand interactions in the 50-nm coiled-coil domain of MukB, the divergent SMC protein found in γ-proteobacteria. Here, we apply that technique to map the structure of the Bacillus subtilis SMC (BsSMC) coiled-coil domain. We find that, in contrast to the relatively complicated coiled-coil domain of MukB, the BsSMC domain is nearly continuous, with only two detectable coiled-coil interruptions. Near the middle of the domain is a break in coiled-coil structure in which there are three more residues on the C-terminal strand than on the N-terminal strand. Close to the head domain, there is a second break with a significantly longer insertion on the same strand. These results provide an experience base that allows an informed interpretation of the output of coiled-coil prediction algorithms for this family of proteins. A comparison of such predictions suggests that these coiled-coil deviations are highly conserved across SMC types in a wide variety of organisms, including humans.
染色体结构维持（SMC）蛋白构成了多亚基复合物的核心，这些复合物是生命所有领域中染色体分离和整体组织所必需的。这些蛋白质具有共同的结构域结构，其中N端和C端区域相互堆积形成一个球状ATP酶结构域。这个“头部”结构域通过一个长的反平行卷曲螺旋与一个中央球状“铰链”或二聚化结构域相连。迄今为止，对SMC蛋白进行结构表征的大多数努力都集中在球状结构域上。然而，最近我们开发了一种方法来绘制MukB（γ-变形杆菌中发现的不同SMC蛋白）50纳米卷曲螺旋结构域中的链间相互作用图谱。在这里，我们应用该技术来绘制枯草芽孢杆菌SMC（BsSMC）卷曲螺旋结构域的结构。我们发现，与MukB相对复杂的卷曲螺旋结构域不同，BsSMC结构域几乎是连续的，只有两个可检测到的卷曲螺旋中断。在该结构域的中部附近，卷曲螺旋结构有一个断裂，其中C端链上的残基比N端链上多三个。靠近头部结构域，有第二个断裂，同一条链上有一个长得多的插入序列。这些结果提供了一个经验基础，有助于对该蛋白家族的卷曲螺旋预测算法的输出结果进行明智的解读。对这些预测结果的比较表明，这些卷曲螺旋偏差在包括人类在内的多种生物的不同SMC类型中高度保守。
