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

Prion假说认为，正常细胞内的Prion蛋白的异常构象是导致包括人类遗传病CJB在内的几种致命性神经退行性疾病的感染因子的基本成分，可能是唯一的。Prion蛋白的N末端区域包含5个串联重复序列，其共有序列为PHGGGWGQ。在水中对包括C^1R^2Q^3P^4H^5G^6G^7S^8W^9G^&lt；10&gt；Q^&lt；11&gt；R^&lt；12&gt；D^&lt；13&gt；C^&lt；14&gt；(L1)在内的四个肽进行了核磁共振研究。这四种多肽模拟物的C_αH化学位移差异与其他研究人员观察到的人类PrP蛋白串联重复序列的差异非常相似。在H5的C_βH和L1的W9侧链质子之间发现了中等范围的NOE连接性。这些观察结果表明，组氨酸(I)与色氨酸(I，4)密切相关。结构计算表明，cyclo-[C^1R^2D^3Y^4S^5P^6T^7S^8P^9S^&lt；10&gt；Y^&lt；11&gt；S^&lt；(G/S)W和(G/S)WGQ分别采用环状构象和β-TURN构象。RNA聚合酶II的羧基末端结构域富含磷酸化位点，含有17-52个串联重复序列，与七肽YSPTSPS的共有序列相同。该七肽的重复单元具有两个SPXX基序，分别为SPTS和SPSY.在pH值为4.0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12&>；R^&lt；13；D^&lt；14&>；C^&lt；15&>]和cyclo-[C^1R^2D^3Y^4S^5P^6T^7S^8P^9S^&lt；10&gt；Y^&lt；11&gt；S^&lt；12&gt；P^&lt；13&gt；T^&lt；14&gt；S^&lt；15&gt；P^&lt；16&gt；N^&lt；17&gt；Y^&lt；18&gt；S^&lt；19&gt；R^&lt；20&gt；D^&lt；21&gt；C^&lt；22&gt；]。通过分子动力学和能量最小化方法得到了与包括NOE距离在内的核磁共振参数一致的构象。这些计算为SPTS部分产生了两个稳定的构象。两者中的一个对应于类型Iβ-Turn。

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.