PROBING NUCLEOTIDE DEPENDENT CONFORMATIONAL CHANGE IN THE NITROGENASE FE PROTEIN

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。在固氮酶催化过程中，铁蛋白和铼-铁蛋白以导致两个MgATP分子水解和至少一个电子转移到MoFe蛋白的方式缔合和解离。这些核苷酸依赖的构象变化是类似的生化信号转导机制的一些其他的例子，因此探测的作用，三磷酸核苷结合和水解固氮酶是具有广泛的意义。有相当多的生物化学和光谱学证据，包括小角度X射线散射研究，表明Fe蛋白在核苷酸置换（MgATP置换MgADP或核苷三磷酸水解）过程中发生构象变化。 我们最近已经确定了一个站点的直接变体的Fe蛋白的结构，具有一些生化和光谱特征的情况下，类似于天然Fe蛋白的存在下，结合MgATP的核苷酸。分离Fe蛋白变体和Fe蛋白的上述结构的最显著的结构差异在很大程度上表现为Fe蛋白亚基相对于彼此的刚体重定向。每个Fe蛋白亚基通过相对于先前表征的Fe蛋白结构相对于彼此大约60至80度的刚体旋转而重新取向。 我们使用晶体学坐标的计算表明，尽管在变体中缺少残基，但位点直接变体的回转半径比天然Fe蛋白大约2.2。这一结果显然与之前关于MgATP结合后天然蛋白质的SAXS结果相矛盾[Chen et al.，（1994）J.Biol.Chem.269，3290]。我们希望重新审视核苷酸结合态天然Fe蛋白的SAXS，以检验我们假设的Fe蛋白构象变化模型的有效性，

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. During nitrogenase catalysis, the iron protein and molybdenum-iron protein associate and dissociate in a manner resulting in the hydrolysis of two molecules of MgATP and the transfer of at least one electron to the MoFe protein. These nucleotide dependent conformational changes are analogous to a number of other examples of biochemical signal transduction machinery and therefore probing the role of nucleoside triphosphate binding and hydrolysis in nitrogenase is of broad significance. There is considerable biochemical and spectroscopic evidence including small angle x-ray scattering studies that have implicate that the Fe protein undergoes conformational changes during nucleotide displacement (MgATP for MgADP or nucleoside triphosphate hydrolysis. We have recently determined the structure of a site-direct variant of the Fe protein that has a number of biochemical and spectroscopic features in the absence of nucleotide that resemble the native Fe protein in the presence of bound MgATP. The most significant structural differences that separate the Fe protein variant and the aforementioned structures of the Fe protein are largely manifested in a rigid body reorientation of the Fe protein subunits with respect to one another. Each of the Fe protein subunits is reoriented by a rigid-body rotation with respect to one another on the order of sixty to eighty degrees relative to the previously characterized Fe protein structures. Our calculation using the crystallographic coordinates indicates that the site-direct variant has a radius of gyration approximately 2.2 ¿¿larger than that of the native Fe protein despite the missing residues in the variant. This result apparently contradicts the previous SAXS results on the native protein upon MgATP binding [Chen et al., (1994) J. Biol. Chem. 269, 3290]. We would like to revisit SAXS of the native Fe protein in nucleotide bound states to examine the validity of our hypothetical model for the conformational changes the Fe protein und