Bousset L, Belrhali H, Janin J, Melki R, Morera S
Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
Structure. 2001 Jan 10;9(1):39-46. doi: 10.1016/s0969-2126(00)00553-0.
The [URE3] non-Mendelian element of the yeast S. cerevisiae is due to the propagation of a transmissible form of the protein Ure2. The infectivity of Ure2p is thought to originate from a conformational change of the normal form of the prion protein. This conformational change generates a form of Ure2p that assembles into amyloid fibrils. Hence, knowledge of the three-dimensional structure of prion proteins such as Ure2p should help in understanding the mechanism of amyloid formation associated with a number of neurodegenerative diseases.
Here we report the three-dimensional crystal structure of the globular region of Ure2p (residues 95--354), also called the functional region, solved at 2.5 A resolution by the MAD method. The structure of Ure2p 95--354 shows a two-domain protein forming a globular dimer. The N-terminal domain is composed of a central 4 strand beta sheet flanked by four alpha helices, two on each side. In contrast, the C-terminal domain is entirely alpha-helical. The fold of Ure2p 95--354 resembles that of the beta class glutathione S-transferases (GST), in line with a weak similarity in the amino acid sequence that exists between these proteins. Ure2p dimerizes as GST does and possesses a potential ligand binding site, although it lacks GST activity.
The structure of the functional region of Ure2p is the first crystal structure of a prion protein. Structure comparisons between Ure2p 95--354 and GST identified a 32 amino acid residues cap region in Ure2p exposed to the solvent. The cap region is highly flexible and may interact with the N-terminal region of the partner subunit in the dimer. The implication of this interaction in the assembly of Ure2p into amyloid fibrils is discussed.
酿酒酵母的[URE3]非孟德尔遗传元件是由朊病毒蛋白Ure2的一种可传播形式的增殖引起的。Ure2p的传染性被认为源于朊病毒蛋白正常形式的构象变化。这种构象变化产生了一种能组装成淀粉样纤维的Ure2p形式。因此，了解诸如Ure2p等朊病毒蛋白的三维结构应有助于理解与许多神经退行性疾病相关的淀粉样蛋白形成机制。
在此我们报告了Ure2p球状区域（第95 - 354位氨基酸残基）的三维晶体结构，该区域也称为功能区域，通过多波长反常散射（MAD）方法在2.5埃分辨率下解析得到。Ure2p 95 - 354的结构显示为一种形成球状二聚体的双结构域蛋白。N端结构域由一个中央的4股β折叠片层组成，两侧各有四个α螺旋。相比之下，C端结构域完全由α螺旋组成。Ure2p 95 - 354的折叠类似于β类谷胱甘肽S - 转移酶（GST），这与这些蛋白质之间存在的氨基酸序列弱相似性一致。Ure2p像GST一样形成二聚体，并且具有一个潜在的配体结合位点，尽管它缺乏GST活性。
Ure2p功能区域的结构是朊病毒蛋白的首个晶体结构。Ure2p 95 - 354与GST之间的结构比较确定了Ure2p中一个暴露于溶剂的32个氨基酸残基的帽状区域。帽状区域高度灵活，可能与二聚体中伙伴亚基的N端区域相互作用。讨论了这种相互作用在Ure2p组装成淀粉样纤维中的意义。
