title: Different isoforms and post-translational modifications of human salivary acidic proline-rich proteins.
abstract: The human salivary acidic proline-rich proteins (aPRPs) complex was investigated by different chromatographic and mass spectrometric approaches and the main aPRPs, namely PRP-1, PRP-2 and PIF-s (15,515 amu), Db-s (17,632 amu) and Pa (15,462 amu) proteins, were detected. All these isoforms are phosphorylated at Ser-8 and Ser-22 and have a pyroglutamic moiety at the N-terminus. Apart from Pa, all the other aPRPs undergo a proteolytic cleavage at Arg-106 residue (Arg-127 in Db-s protein), that generates the small PC peptide (4371 amu) and PRP-3, PRP-4, PIF-f (11,162 amu) and Db-f (13,280 amu) proteins, all of which were detected. With regard to the Pa protein, the main form detected was the dimeric derivative (Pa 2-mer, 30,922 amu) originated by a disulfide bond involving Cys-103 residue. Besides these known isoforms, several previously undetected aPRP derivatives were found (in minor amounts): (i) the triphosphorylated derivatives of PRP-1/PRP-2/PIF-s and Db-s, showing the additional phosphate group at Ser-17; (ii) the mono-phosphorylated forms at either Ser-22 or Ser-8 of PRP-1/PRP-2/PIF-s, PRP-3/PRP-4/PIF-f, Db-s and Db-f; (iii) a nonphosphorylated form of PRP-3/PRP-4/PIF-f; (iv) the triphosphorylated and diphosphorylated forms of Pa 2-mer. Moreover, minor quantities of PRP-3/PRP-4/PIF-f lacking the C-terminal Arg (11,006 amu), and of Pa 2-mer lacking the C-terminal Gln (30,793 amu) were found. By this approach the different phenotypes of PRH1 locus in 59 different subjects were characterized.
authors.affiliation: Istituto di Biochimica e Biochimica Clinica, Facoltà di Medicina, Università Cattolica, Rome, Italy.
authors.forename: Rosanna
authors.initials: R
authors.lastname: Inzitari
authors.forename: Tiziana
authors.initials: T
authors.lastname: Cabras
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Onnis
authors.forename: Chiara
authors.initials: C
authors.lastname: Olmi
authors.forename: Andrea
authors.initials: A
authors.lastname: Mastinu
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Sanna
authors.forename: Maria Guiseppina
authors.initials: MG
authors.lastname: Pellegrini
authors.forename: Massimo
authors.initials: M
authors.lastname: Castagnola
authors.forename: Irene
authors.initials: I
authors.lastname: Messana
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis* / Q000378:metabolism; D010750:Phosphoproteins / Q000032:analysis*; D055232:Proline-Rich Protein Domains; D020033:Protein Isoforms / Q000032:analysis / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D055273:Salivary Proline-Rich Proteins; D012471:Salivary Proteins and Peptides / Q000032:analysis* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: C524536:PRH1 protein, human; D010455:Peptides; D010750:Phosphoproteins; D020033:Protein Isoforms; D055273:Salivary Proline-Rich Proteins; D012471:Salivary Proteins and Peptides