Thermodynamic and kinetic studies of macromolec structure and enzymic mechanisms

(I)对淀粉样多肽和蛋白质结构的光学研究仍在继续。我们特别感兴趣的是与淀粉样蛋白纤维的交叉β结构有关的非常强烈的CD光谱的来源。这一现象表现在已被证明形成具有平行和反平行β片状结构的淀粉样蛋白的多肽上。 (Ii)与T.K.Daie和B.Chen(大学)小组合作。，我们研究了一种小的惰性共溶质三甲胺氧化物(TMAO)在代谢物S-腺苷-蛋氨酸(SAM)和镁离子浓度增加的情况下对SAM II核糖开关构象变化的影响。在没有SAM和Mg++的情况下，游离核糖开关呈开放或半无规构象，结合SAM和/或Mg++后，核糖开关变得更加折叠和致密。大量测量核糖开关的圆二色谱与这些小配体的浓度的依赖关系可以用一个模型定量地解释，根据该模型，SAM只与紧凑的构象结合。在没有SAM的情况下，核糖开关似乎是开态和紧密态的混合体。低浓度的镁离子或氧化三甲胺能结合到开放形式(S)上，从而抑制表面活性物质的结合。在较高浓度下，Mg++的协同结合或TMAO的分子拥挤，使核糖开关转变为致密形式，有利于SAM的结合。镁离子的进一步结合增加了紧凑形式的核糖开关对SAM的亲和力。流体力学测试表明，该核糖开关被浓缩的TMAO压实。 (3)碳纳米管结构的光学研究。

(i) Optical studies on the structures of amyloid peptides and proteins are continuing.We are particularly interested in origin of the very intense CD spectrum which has been associated with the cross-beta structure of amyloid fibrils. This phenomenon is shown by peptides which have been shown to form amyloid with both parallel and anti-parallel beta sheet structure. (ii) In collaboration with the group of T. K. Dayie and B. Chen (Univ. of MD), we have investigated the effect of a small inert cosolute, trimethylamine oxide (TMAO), on the conformational changes of the SAM II riboswitch in the presence of increasing concentrations of the metabolite S-adenosyl-methionine (SAM) and Mg++. The free riboswitch was thought to be in an open or semi-random conformation in the absence of SAM and Mg++ and to become more folded and compact upon binding SAM and/or Mg++. Extensive measurements of the dependence of circular dichroism spectra of the riboswitch upon the concentrations of these small ligands may be quantitatively accounted for by a model, according to which SAM binds exclusively to a compact conformation. In the absence of SAM, the riboswitch seems to be a mixture of open and compact states. Low concentrations of Mg++ or TMAO bind to the open form(s), inhibiting the binding of SAM. At higher concentrations, cooperative binding of Mg++ or molecular crowding by TMAO, transform the riboswitch into the compact form, facilitating the binding of SAM. Further binding of Mg++ increases the affinity of the compact form of the riboswitch for SAM. Hydrodynamic measurements show that the riboswitch is compacted by concentrated TMAO. (iii) Optical studies on the structure of carbon nanotubes.