Studying the functioning of two diverse biological systems by solution NMR: The PTH receptors and the PDZ1 domain of PSD95/SAP9

Since the pioneering work of Wuthrich in the seventies, NMR spectroscopy has been widely used to evaluate the conformational and dynamical features of biomolecules in solution. Here we applied this technique to investigate two different biological systems, the Parathyroid hormone receptor systems and the PDZ1 domain of PSD95/SAP90.;The PTH1 protein belongs to the G-protein coupled receptor family and by responding to the PTH hormone and PTHrP protein plays a role in a variety of biological processes including calcium level regulation and bone growth. The PTH2 receptor is sequentially homologous to PTH1 and is localized primarily in the central nervous system although its exact function is not completely understood. The structure of the first extracellular loop of the PTH1 receptor, that has been shown to be involved in the hormone recognition process, is presented here, together with the conformations of a family of novel PTH1 ligands capable to bind and activate the PTH1 receptor. Furthermore we also investigated TIP39, the endogenous hormone of the PTH2 receptor, together with the antagonist TIP(7-39). Dodecylphosphocholine micelles have been employed to reproduce, in an experimental system suitable for high resolution NMR studies, the membrane environment. Our results allow a deeper understanding of the molecular mechanism regulating the signaling of PTH receptors.;The PSD95/SAP90 protein is critical for the assembly of the ion channels in the post-synaptic density region of glutamatergic neuron, and for coupling the channels activity to the downstream machinery. The three PDZ domains of PSD95/SAP90 bind the C-terminus of several target proteins. Although highly homologous, each domain exhibits its own unique selectivity. We investigated the recognition mechanism of PDZ1 domain of PSD95/SAP90 by solving the three dimensional structure in solution of this protein alone, and in the presence of the C-termini of the Kv1.4 potassium channel, CRIPT protein, and the GluR6 subunit of kainate receptor. The results reported here reveal a novel binding interaction mode for this class of PDZ domains. The PDZ1 domain was also studied in the presence of a non-natural peptide in the effort of designing new molecules with higher target specificity.