Protein Phosphorylation as a Biophysical Switch: NMR Determination of Structural and Dynamic Responses to Phosphorylation

本研究探讨了可逆磷酸化对蛋白质调控的生物物理基础。高分辨率多维核磁共振（NMR）技术将用于阐明模型系统中蛋白质磷酸化的结构和动态方面。研究人员将研究来自鸡c-Src （Src）的两个包含关键调控结构域的蛋白片段，以研究在该系统中负责控制的生物物理机制。由Src-homology 3 （SH3）和Src-homology 2 （SH2）结构域组成的第一个片段的结构和动力学的确定将有双重目的：a)它将为构建更大的Src片段的更高级研究提供基础；b)它将使鉴定分子内相互作用成为可能，这可能有助于最近确定的SH3结构域在稳定SH2/磷酸肽相互作用中的作用。第二个更大的片段包含80个残基，这些残基组成了Src独特的n端区域，将用于研究该蛋白对磷酸化的结构和动态响应。该片段含有特定的磷酸化位点，已知可调节Src的酪氨酸激酶活性。该蛋白片段在磷酸化和非磷酸化状态下的结构和动力学将使用现在标准的多维技术进行研究。这些研究将揭示被破坏的相互作用和那些由磷酸化形成的相互作用，并将从原子水平上观察这种重要的共价修饰在这些共同调控模块中引起的变化。已知蛋白磷酸化参与多种生物过程的控制，包括代谢、细胞增殖和分化、膜转运、基因表达、运动、记忆和学习。然而，只有两种蛋白的磷酸化调控的生物物理基础是明确建立的，这两种蛋白都表现出不同的控制机制。因此，磷酸化和非磷酸化状态下模型系统的高分辨率结构测定将提供急需的信息，有助于理解这种普遍存在的蛋白质调节开关的原子水平事件。相对较小的保守蛋白结构域，以Src-homology 2 （SH2）和Src-homology 3 （SH3）结构域为典型，存在于大量的信号蛋白中，并已被证明可以作为模块结合结构域，介导分子间和分子内相互作用。Src蛋白是一种细胞原癌蛋白和酪氨酸激酶范例蛋白，包含SH3和SH2结构域以及几个不同的调节磷酸化位点。在Src中，SH2相互作用已被证明是由附近的SH3结构域和位于初级序列中的特定Ser和残基的磷酸化介导的。拟议的研究涉及磷酸化和非磷酸化形式的Src调控装置的结构和动力学研究，并将采用最近开发的高分辨率多维核磁共振波谱技术。总的来说，这些研究将使磷酸化调节蛋白质的结构、动力学和功能之间的关系得以建立，并将对许多其他利用磷酸化作为生物物理开关的蛋白质产生广泛的影响。

This research addresses the biophysical basis of protein regulation by reversible phosphorylation. High resolution multidimensional nuclear magnetic resonance (NMR) techniques will be employed to elucidate the structural and dynamic aspects of protein phosphorylation in a model system. Two protein fragments derived from chicken c-Src (Src) that contain key regulatory domains will be studied to investigate the biophysical mechanisms responsible for control in this system. Determination of the structure and dynamics of the first fragment, composed of the Src- homology 3 (SH3) and Src-homology 2 (SH2) domains, will serve a dual purpose: a) it will provide a foundation on which to build more adva nced studies of larger fragments of Src, and b) it will enableidentification of intramolecular interactions that may contribute to the recently established role of the SH3 domain in stabilizing SH2/phosphopeptide interactions. The second and larger fragment, which has an additional 80 residues that comprise the unique N-terminal region of Src, will be utilized to investigate the structural and dynamic response of the protein to phosphorylation. This fragment contains specific phosphorylation sites that are known to regulate the tyrosine kinase activity of Src. The structure and dynamics of this protein fragment in phosphorylated and unphosphorylated states will be pursued using the now-standard multidimensional techniques. These studies will reveal interactions that are disrupted and those that are formed by phosphorylation, and will provide an atomic level view of the changes induced in these common regulatory modules by this important covalent modification. %%% Protein phosphorylation is known to be involved in the control of a diverse array of biological processes, including metabolism, cell proliferation and differentiation, membrane transport, gene expression, locomotion, memory, and learning. However, the biophysical basis of regulation by phosphorylation is clearly established for only two proteins, both of which exhibit different mechanisms of control. Hence, high resolution structure determinations of a model system in phosphorylated and unphosphorylated states will provide much needed information that will aid in understanding of the atomic level events responsible for this ubiquitous protein regulatory switch. Relatively small, conserved protein domains, typified by the Src-homology 2 (SH2) and Src-homology 3 (SH3) domains, are found in a large number of signaling proteins and have been shown to function as modular binding domains that can mediate both inter-and intramolecular interactions. The Src protein, a cellular proto-oncoprotein and a paradigm protein-tyrosine kinase, con tains both SH3 and SH2 domains as well as several different regulatory phosphorylation sites. In Src, SH2 interactions have been shown to be mediated by nearby SH3 domains and by phosphorylation of specific Ser and The residues remotely located in the primary sequence. The proposed research involves structural and dynamics studies of the Src regulatory apparatus in phosphorylated and unphosphorylated forms, and will employ recently developed high resolution multidimensional NMR spectroscopic techniques. Overall, these studies will enable relationships between structure, dynamics and function in a protein regulated by phosphoylation to be established, and will have broad implications for numerous other proteins that utilize phosphorylation as a biophysical switch.