TIME EVOLUTION OF THE ALLOSTERIC TRANSITION OF ASPARTATE TRANSCARBAMOYLASE

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。天冬氨酸转氨甲酰酶。大肠杆菌存在两种构象状态，低活性低亲和力T状态和高活性高亲和力R状态。该酶不仅催化嘧啶生物合成途径中的第一个反应，而且还参与控制整个代谢途径的速率。控制被认为是通过改变T和R形式的比例来实现的。酶的T和R状态在功能和结构上都是不同的。在酶从T状态转变为R状态的过程中，酶经历了约11沿着的延伸，同时伴随着亚基的旋转，这可以很容易地被SAXS检测到。我们以前提出了一个协调的变构过渡的T到R状态的机制。我们已经能够在SSRL使用时间分辨SAXS进行一组实验，以直接跟踪从T到R状态的结构转变的时间过程。这些初步数据表明，在过渡过程中形成了结构中间体。该建议是在SSRL的额外的光束时间，以继续调查的酶的变构机制，以及异向效应如何影响从T到R状态的结构转变。这将是第一次变构酶的变构结构变化的时间演变将遵循真实的时间SAXS。

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. Aspartate transcarbamoylase from E. coli exits in two conformational states, a low-activity low-affinity T state and a high-activity high-affinity R state. The enzyme not only catalyzes the first reaction in the pyrimidine biosynthesis pathway, but is also involved in the control of the rate of this entire metabolic pathway. Control is thought to be achieved by altering the ratio of the T and R forms. The T and R states of the enzyme are both functionally and structurally distinct. During the conversion of the enzyme from the T to the R state, the enzyme undergoes an elongation of appoximately 11 ¿¿ along with simultaneous rotations of subunits, which can easily be detected by SAXS. We have previously proposed a mechanism for a concerted allosteric transition from the T to the R states. We have been able to perform one set of experiments at SSRL using time-resolved SAXS to directly follow the time course of the structural transition from the T to the R state. These preliminary data suggest that a structural intermediate is formed during the transition. This proposal is for additional beam time at SSRL to continue the investigation into the allosteric mechanism of the enzyme and how the heterotropic effects influence the structural transition from the T to the R state. This will be the first time for an allosteric enzyme that the time evolution of the allosteric structural change will be followed in real time by SAXS.