Extensive proteomics characterization of basic proline-rich proteins in human saliva and investigation on their properties as substrates of epithelial transglutaminase 2

This PhD thesis describes the work carried out during three years upon the Department of “Scienze della Vita e dell’Ambiente” of the Cagliari University, work that was also partly performed upon the “Istituto di Biochimica e Biochimica Clinica” of the Faculty of Medicine of the Catholic University of Rome. Topics of the thesis were centered on the structural and functional characterization of some human salivary proteins. In particular, the topics investigated were the following: a) Extensive identification of the components of the family of basic (and glycosylated basic) proline-rich proteins (bPRPs and gPRPs), the most complex and heterogeneous family of the human salivary proteins, by a proteomic top-down platform with the aim to achieve the most complete knowledge possible of the main parent proteins present in human saliva and of their post-translational modifications. This study allowed the characterization of 55 new components of the family bringing the total number of naturally occurring components to 110. b) Exploration of the reactivity in vitro of some bPRPs (P-C, P-H, P-D, P-D P32⟶A, II-2, P-F and P-J) as substrate of the epithelial transglutaminase-2 (TG-2). The aim of this study was to establish whether these bPRPs can potentially contribute in vivo to the formation of the “oral mucosal protein pellicle”, a protein network covering the oral mucosal epithelia devoted to the protection of the oral cavity. This study allowed establish that almost all the bPRPs are substrates of TG-2 and therefore are potential components of the “oral mucosal protein pellicle” and that, despite the great sequence similarity, their reactivity is significantly different.