Biophysics of Macromolecular Complexes

染色质结构和构筑。 细胞核内的DNA被包装成染色质，目前有多种模型描述了浓缩的30 nm染色质纤维的结构。我们特别感兴趣的是了解DNA在浓缩的30 nm染色质片段中的拓扑结构。为了做到这一点，我们目前正在开发高分辨率的染色体捕获构象分析，利用体外模型系统以及天然染色质片段，例如以前研究的浓缩异染色质，侧翼是发育调节的叶酸受体和β-珠蛋白基因。这些研究将使我们能够确定30 nm染色质纤维的结构，这反过来将提供更好的理解染色质结构与基因表达和DNA复制等基本过程之间的关系。 大分子组装。 在与分子生物学实验室成员和其他人的合作下，利用流体力学方法对蛋白质和蛋白质-核酸组件的形状、化学计量和相互作用的亲和力进行了表征。这些研究扩展了目前的生化和结构研究，最近发表的关于单价凝集素微病毒的研究就是例证，这些研究是与G.Marius Clore博士和Carole Bewley博士合作进行的。 在这项研究中，纯化的微病毒唑以单分散单体的形式与甘露糖α(1-2)甘露糖单价结合，亲和力为50微摩尔。当这个双糖单元终止高甘露糖N连接碳水化合物链的手臂时，微病毒能够与高度糖基化的HIV-1表面蛋白gp120相互作用，阻止HIV-1进入培养细胞。这些生物物理和结构研究阐明了微病毒抑制艾滋病毒进入的分子机制(Shahzad-ul-Hussan等人，2011年)。

Chromatin structure and architecture. DNA within the cell nucleus is packaged into chromatin and a variety of models presently describe the structure of the condensed 30 nm chromatin fiber. We are specifically interested in an understanding of the topological organization of DNA within condensed 30 nm chromatin fragments. In order to do this we are currently developing high resolution chromosome capture conformation assays utilizing both in vitro model systems, as well as native chromatin fragments, such as the previously studied condensed heterochromatin flanked by the developmentally regulated folate receptor and beta-globin genes. These studies will allow us to determine the structure of the 30 nm chromatin fiber, which will in turn provide a better understanding of the relations between chromatin structure and essential processes such as gene expression and DNA replication. Macromolecular assemblies. In collaboration with members of the Laboratory of Molecular Biology, and others, protein and protein-nucleic acid assemblies have been characterized in terms of their shape, stoichiometry and affinity of interaction using hydrodynamic methods. These studies extend current biochemical and structural investigations as exemplified by recently published studies on the monovalent lectin microvirin carried out in collaboration with Drs. G. Marius Clore and Carole Bewley. In this study, purified microvirin was shown to exist as a monodisperse monomer which binds monovalently to mannose alpha(1-2) mannose with an affinity of 50 micromolar. As this disaccharide unit terminates the arms of high mannose N-linked carbohydrate chains, microvirin is able to interact with the highly glycosylated HIV-1 surface protein gp120 and prevent HIV-1 entry into cultured cells. These biophysical and structural studies illustrate the molecular mechanism through which microvirin inhibits HIV entry (Shahzad-ul-Hussan et al., 2011).