Lea S, Powell R, Evans D
Laboratory of Molecular Biophysics, Rex Richards Building, South Parks Road, Oxford OX1 3QU, England.
Acta Crystallogr D Biol Crystallogr. 1999 Jun;55(Pt 6):1198-200. doi: 10.1107/s0907444999001638.
Crystals have been grown of two of the domains of CD55. This is the first report of crystallization of a short consensus repeat (SCR) domain containing protein. CD55 is a widely expressed polymorphic glycoprotein, which functions as a complement regulator by inhibiting assembly and promoting destruction of C3 and C5 convertases. As a key regulator of complement, CD55 is implicated in the hyperacute rejection of xenografts from pigs into primates. It is also commonly hijacked as a receptor by viruses (e.g. medically important echoviruses and coxsackieviruses) and bacterial pathogens (e.g. certain pathogenic strains of Escherichia coli). Here, crystallization of a virus-binding fragment expressed in yeast, consisting of two of the four extracellular SCR domains of CD55, is reported. The recombinant domains have been crystallized in 30% polyethylene glycol (PEG), 0.2 M sodium acetate, 0.1 M sodium acetate trihydrate pH 4.6 using the sitting-drop vapour-diffusion method. Two crystal forms are observed (orthorhombic and monoclinic) and a native data set to 1.65 A resolution has been collected from the monoclinic form at the Synchrotron Radiation Source, Daresbury, UK.
已培养出CD55两个结构域的晶体。这是关于含短共有重复序列（SCR）结构域蛋白质结晶的首次报道。CD55是一种广泛表达的多态性糖蛋白，通过抑制C3和C5转化酶的组装并促进其降解来发挥补体调节作用。作为补体的关键调节因子，CD55与猪到灵长类动物的异种移植超急性排斥反应有关。它还常被病毒（如具有医学重要性的艾柯病毒和柯萨奇病毒）和细菌病原体（如某些致病性大肠杆菌菌株）劫持作为受体。在此，报道了在酵母中表达的病毒结合片段的结晶情况，该片段由CD55的四个细胞外SCR结构域中的两个组成。使用坐滴气相扩散法，重组结构域已在30%聚乙二醇（PEG）、0.2 M醋酸钠、0.1 M三水合醋酸钠pH 4.6中结晶。观察到两种晶体形式（正交晶系和单斜晶系），并在英国达雷斯伯里的同步辐射源从单斜晶系形式收集到了分辨率为1.65 Å的天然数据集。
