Three-dimensional structure of tandem repeats within RNA polymerase II, prion, and LEA proteins

“朊病毒假说”认为，正常细胞朊病毒蛋白的异常构象是导致几种致命的神经退行性疾病（包括人类遗传性疾病CJB）的感染因子的必要成分，也许是唯一成分。朊病毒蛋白n端包含5个串联重复序列，一致序列为PHGGGWGQ。在水中对四种肽进行了核磁共振研究，包括C^1R^2Q^3P^4H^5G^6G^7S^8W^9G^<10>Q^<11>R^<12>D^<13>C^<14> (L1)。这四种多肽模拟物的C_αH化学位移差异模式与其他研究人员对人类朊蛋白串联重复序列的观察结果非常相似。在H5的C_βH和L1的W9侧链的质子之间发现了中等范围的NOE连通性。这些观察结果表明，组氨酸(i)与色氨酸（i+4）非常接近。L1的结构计算表明，HGG (G/S) W和（G/S） WGQ分别为环状构象和β-转构象。RNA聚合酶II的羧基末端结构域（CTD）富含磷酸化位点，包含17-52个串联重复序列，与七肽的一致序列YSPTSPS一致。七肽的重复单元有两个显示潜在β-转变的SPXX基序，SPTS和SPSY。在pH4.0的水中对含有一个和两个重复单元的两个环肽进行了核磁共振研究，cyclo-[C^1R^2D^3Y^4S^5P^6T^ 7p ^8P^9S^<10>Y^<11>S^<12>R^<13>D^<14>C^<15>]和cyclo-[C^1R^2D^3Y^4S^5P^6T^ 8P^9S^<10>Y^<11>S^<12>P^<13>T^<14>S^<15>P^<16>N^<17>Y^<18>S^<19>R^<20>D^<21>C^<22>]。通过分子动力学和能量最小化方法获得了与核磁共振参数（包括NOE距离）一致的构象。这些计算为SPTS段产生了两个稳定的构象。其中一个对应于I型β转。

The "prion hypothesis" holds that an aberrant conformation of a normal cellular prion protein is the essential, perhaps sole, component of infection agent responsible for several fatal neurodegenerative diseases, including the human genetic disease CJB.The N-terminal region of the prion protein contains five tandem repeats with the consensus sequence of PHGGGWGQ.NMR studies were performed in water for four peptides including C^1R^2Q^3P^4H^5G^6G^7S^8W^9G^<10>Q^<11>R^<12>D^<13>C^<14> (L1). The patterns of the C_αH chemical shift difference of these four peptide mimetics were very similar to those observed for the tandem repeats of human prion protein reported by other researchers. The medium-range NOE connectivities were found between the C_βH of the H5 and the proton of the W9 side chain for L1. These observations indicate that histidine (i) is in close proximity to tryptophan (i+4). Structure calculations for L1 showed that HGG (G/S) W and (G/S) WGQ adopt a loop conformation and a β-turn, respectively.The carboxyl terminal domain (CTD) of RNA polymerase II, which is rich in phosphorylation sites, contains 17-52 tandem repeats with the consensus sequence of the heptapeptide, YSPTSPS.The repeat unit of the heptapeptide has two SPXX motifs showing potential β-turns, SPTS and SPSY.NMR studies were performed in water at pH4.0 for two cyclic peptides containing one and two repeat units, cyclo-[C^1R^2D^3Y^4S^5P^6T^7S^8P^9S^<10>Y^<11>S^<12>R^<13>D^<14>C^<15>] and cyclo-[C^1R^2D^3Y^4S^5P^6T^7S^8P^9S^<10>Y^<11>S^<12>P^<13>T^<14>S^<15>P^<16>N^<17>Y^<18>S^<19>R^<20>D^<21>C^<22>]. Conformations consistent with NMR parameters including NOE distances were obtained through molecular dynamics and energy minimization methods. These calculations yielded two stable conformers for the SPTS segment. One of the two corresponds to a type I β-turn.