Mpro-C蛋白三维结构域交换的机理:来自分子模拟的线索

SARS coronavirus main protease (Mpro) is a key enzyme involved in the extensive proteolytic processing of the virus? polyproteins. The crystal structure of Mpro reveals that the enzyme exists in two different homo-dimeric forms: a three-dimensional (3D) domain-swapped form; and a non-3D domain-swapped form. The isolated C-terminal domain (Mpro-C) also forms a 3D domain-swapped structure similar to the ful-length protein. Unlike conventional 3D domain-swapped structures, in which the swapped regions are located on the surface, Mpro-C swaps a helix at the core of a folded domain. In this work, we used molecular dynamics simulations and 3D domain-swapping predictions to investigate how a highly buried core helix in the helix bundle structure of Mpro-C can be swapped. We found that both structure-and sequence-based methods failed to predict the location of the hinge loop in Mpro-C and Mpro. Extensive molecular dynamics simulations were performed to investigate the structural properties of the unfolded monomer and the 3D domain-swapped dimer of Mpro-C. We found that, although the swapped region was buried in the native state, it was exposed in the unfolded monomer. Our results suggest that the opening of the swapped region in the ful y or partial y unfolded state may promote interactions between monomers and the formation of domain-swapped dimers.     

Mpro-C蛋白三维结构域交换的机理: 来自分子模拟的线索

SARS冠状病毒主蛋白酶(M^pro)在病毒的蛋白酶切过程中发挥着重要作用. M^pro的晶体结构显示它存在两种形式的二聚体: 一种是发生三维结构域交换的形式, 另一种是非交换的形式. M^pro的C端结构域(M^pro-C)单独表达时也能形成与全长M^pro类似的三维结构域交换二聚体. 三维结构域交换通常发生在蛋白质的表面, 但M^pro-C 的结构域交换却发生在疏水核心. 在本文中, 我们利用分子动力学模拟及三维结构域交换预测算法研究了M^pro-C 中被高度埋藏的核心螺旋片段发生交换的机理. 我们发现基于结构与基于序列的已有算法都不能正确预言出M^pro-C和M^pro中发生结构域交换的铰链区位置. 分子模拟结果表明M^pro-C中的交换片段在天然态下埋藏得很好, 但在变性单体中则会被释放并暴露在外面. 因此, 在完全或部分解折叠状态下交换片段的打开有助于促进单体间的相互作用及结构域交换二聚体的形成.     

不同实验条件对锰矿法制备介孔纳米四氧化三锰性能的影响

采用简单易行,成本低廉的锰矿法,以软锰矿焙烧熟料溶出液为原料,氨水为沉淀剂,空气为氧化剂,制备四氧化三锰.研究了不同实验条件对Mn3 O4物相、形貌、比表面积的影响,采用XRD、SEM和BET对产物进行表征.结果表明,不同的实验条件对所得产物物相组成没有明显影响,经过超声处理的样品结晶度更好;不同的实验条件所得产物均为介孔结构的纳米级四氧化三锰,但对产物形貌和比表面积有较大影响.实验最佳条件为:不经过超声,未加任何添加剂,MnSO4反加到NH3·H2 O中的沉淀-氧化两步法.所得产物由球状颗粒和细棒状组成,球状颗粒的粒径最小,大部分小于50 nm,比表面积为35.05 m2/g.     

ZnO半导体电导型X射线探测器件研究

本文制备了基于ZnO纳米线阵列和ZnO薄膜的Ag-ZnO-Ag电导型X射线探测器件,研究了它们对X射线的响应特性.薄膜器件在100 V偏置时的响应度达到0.12μC/Gy,纳米线阵列器件在50 V偏压下的响应度达到0.17μC/Gy.器件工作机理研究表明,器件的响应过程与表面氧吸附与解吸附效应有关,氧气吸附与解吸附过程使得X射线辐照下的载流子寿命大幅度增加,从而使得器件对X射线具有较高的响应度.本文研究结果表明ZnO薄膜和纳米线阵列器件在X射线剂量测量领域具有应用前景.