The role of structural determinants on the biological functions in the peptide-membrane and protein-protein interactions: the solution structure approach

NMR spectroscopy in many of the more recent applications can give relevant information in the study of biomolecular structure and about their interactions. The results of the studies here reported show that in the case of the peptide –membrane and protein –protein interactions NMR spectroscopy often may give many informations about the structural details of the interaction. These results are useful to understand better the mechanism of the intermolecular recognition and/or the conformational change(s) upon binding. In the study of Thymosin α1, a hormone peptide whose specific cellular receptor(s) were not found, Circular Dichroism and NMR spectroscopy techniques revealed that a conformational change of this biomolecule toward a structured form upon interaction with membrane model and cell occurs. Particularly a preference of this hormone was found for phosphatidylserine exposed on membrane surface. The hypothesis that the biological mechanism of action of this hormone may consist in a membrane catalyzed interaction seems valid and this hypothesis may give information about future medical applications in other pathologies. In the study of the proteic domain CUBAN and of its interaction with the ubiquitin-like protein NEDD8 the solution structure of the protein and of its complex has been elucidated. The results obtained by NMR spectroscopy are in agreement with the results of pull-down and mutagenesis experiments. By the observation of the chemical shift perturbations of the 15N HSQC spectra upon addition of proteins revealed the possibility of he existence of an early stage in the interaction. A complex interplay between hydrophobic and polar interactions, driven by structural determinants of the two proteins, was found to be the driving force of the recognition mechanism. The studies reported in this Ph.D thesys were performed in collaboration with two different groups of University of Rome “Tor Vergata”. The elucidation of the interaction of Thymosin-alpha1 with model membranes and cells were performed in collaboration with proff. E. Garaci, P. Sinabaldi Vallebona and F. Pica. The structural investigation of CUBAN domain of KHNYN and the studies of its interaction with NEDD8 protein were developed with the collaboration of doc. E. Santonico and prof. G. Cesrani’s group.