Structure and function of DISC1 in the cAMP pathway

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DISC1 (Disrupted-In-Schizophrenia-1) has emerged as a significant genetic risk factor for a wide range of mental illness such as schizophrenia, bipolar disorders and depression. The product of DISC1 is a long scaffold protein that plays a critical role in several neuronal signaling pathways. Despite growing appreciation of its role in the etiology of mental disorders, almost nothing is known about the structure of DISC1 and its mechanisms of interaction and regulation. This research project will specifically focus on the role of DISC1 in the cAMP pathway. Reduced cAMP levels are found in patients suffering from major depression and are associated with neurodegenerative diseases. Enzymes controlling intracellular levels of cAMP, such as the phosphodiesterase family PDE4, have considerable pharmaceutical importance for the development of antidepressant and memory enhancing drugs. The overall goal of this project is to provide a structural framework describing the role of DISC1 in the cAMP pathway and to understand how alterations in this pathway contribute to the etiology of psychiatric disorders. Aim 1 will provide a complete structural model of DISC1, including its mechanism of oligomerization and modulation by phosphorylation. We will also investigate the structural consequences of disease-associated mutations. We are proposing here an integrative structural approach combining Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS), solution NMR spectroscopy, X-ray crystallography, Small-angle X-ray Scattering (SAXS) and molecular simulations to reconstitute the complete structural and dynamical features of DISC1. Our preliminary data demonstrate that we can characterize DISC1 N-terminal constructs by solution NMR spectroscopy while constructs encompassing the central and/or C-terminal domains are well suited for X- ray crystallography study. Aim 2 will combine biochemical and structural approaches to characterize the interaction between DISC1 and ATF4, a major transcription factor the cAMP pathway controlling the expression of the CRE-elements and of the phosphodiesterase PDE4D9. Our preliminary data show that DISC1-ATF4 complex can be reconstituted in vitro with truncated constructs of both proteins. This aim will provide a mechanistic framework for understanding the role of DISC1 as transcriptional co-repressor and the function of DISC1-ATF4 complex in the cAMP pathway. Aim 3 will unravel the mechanisms of allosteric inhibition of long and short PDE4 isoforms by DISC1, using a combination of biochemical, structural and computational techniques. Overall, completion of this project will provide a comprehensive, unifying framework for understanding the role of DISC1 in the cAMP pathway. Our work will also provide new structural targets for the development of molecules regulating cAMP levels.