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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >A case of structure determination using pseudosymmetry
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A case of structure determination using pseudosymmetry

机译：确定使用的结构伪对称

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Here, a case is presented of an unusual structure determination which was facilitated by the use of pseudosymmetry. Group A streptococcus uses cysteine protease Mac-1 (also known as IdeS) to evade the host immune system. Native Mac-1 was crystallized in the orthorhombic space group P212 12. Surprisingly, crystals of the inactive C94A mutant of Mac-1 displayed monoclinic symmetry with space group P21, despite the use of native orthorhombic Mac-1 microcrystals for seeding. Attempts to solve the structure of the C94A mutant by MAD phasing in the monoclinic space group did not produce an interpretable map. The native Patterson map of the C94A mutant showed two strong peaks along the (1 0 1) diagonal, indicating possible translational pseudosymmetry in space group P21. Interestingly, one-third of the monoclinic reflections obeyed pseudo-orthorhombic P2 1212 symmetry similar to that of the wild-type crystals and could be indexed and processed in this space group. The pseudo-orthorhombic and monoclinic unit cells were related by the following vector operations: am = bo - co,bm = aoand cm = -2co - bo. The pseudo-orthorhombic subset of data produced good SAD phases, leading to structure determination with one monomer in the asymmetric unit. Subsequently, the structure of the Mac-1 mutant in the monoclinic form was determined by molecular replacement, which showed six molecules forming three translationally related dimers aligned along the (1 0 1) diagonal. Knowing the geometric relationship between the pseudo-orthorhombic and the monoclinic unit cells, all six molecules can be generated in the monoclinic unit cell directly without the use of molecular replacement. The current case provides a successful example of the use of pseudosymmetry as a powerful phase-averaging method for structure determination by anomalous diffraction techniques. In particular, a structure can be solved in a higher pseudosymmetry subcell in which an NCS operator becomes a crystallographic operator. The geometrical relationships between the subcell and parental cell can be used to generate a complete molecular representation of the parental asymmetric unit for refinement.
机译：这里提出了一个不同寻常的结构确定了使用伪对称。半胱氨酸蛋白酶Mac-1(也称为ide)逃避宿主的免疫系统。斜方晶系的空间群P212结晶12. 突变的Mac-1显示单斜对称P21和空间群,尽管使用本机斜方晶系的Mac-1微晶核播种。试图解决C94A的结构疯狂的逐步突变体的单斜的空间集团并没有产生一个可判断的地图。本机帕特森C94A突变的地图显示两个强大的山峰(1 0 1)对角线,指示可能转化伪对称P21在空间群。单斜反射的服从1212年pseudo-orthorhombic P2对称相似野生型的晶体和可能索引和处理在这个空间群。pseudo-orthorhombic和单斜单元细胞是由以下相关向量操作:=日宝曼克夫,co = aoand厘米= -2co - bo .pseudo-orthorhombic子集的数据生产好悲伤的阶段,导致结构的决心与一个单体的不对称单元。随后,Mac-1突变体的结构在单斜形态是由分子替换显示,六个分子二聚体形成三个平移相关沿着对角线(1 0 1)一致。几何关系pseudo-orthorhombic和单斜单元细胞,所有六个分子可以在生成不使用直接单斜晶胞分子置换。一个成功的例子,使用伪对称是一个强大的phase-averaging方法由反常衍射结构的决心技术。解决高伪对称子室一个nc运营商成为晶体吗操作符。亚晶胞和亲代细胞可以用来生成一个完整的分子的代表父母的不对称单元细化。

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