Finding new posttranslational modifications in salivary proline-rich proteins.
Proline-rich proteins (PRPs) are the most complex family of salivary peptides with distinct isoforms and PTMs. Up to date, only the serine phosphorylation at positions 8, 17, and 22 have been experimentally observed on acidic PRP (aPRPs), and at position 8 on basic PRP1 and 2. The presence of a glucoronyl group at Ser17 was also noticed on aPRP. The main goal of this study was to identify new PTMs and distinct isoforms of salivary PRPs using LC-MALDI-TOF/TOF. Through the salivary peptidome characterization of 20 different subjects from Control, Diabetic, and Head and Neck Cancer groups, it was possible to identify the following species: (i) N-glycosylation sites: two in basic proline-rich protein 2 (bPRP2), one in bPRP3 and one in bPRP4; (ii) O-glycosylation sites: two in bPRP2 and one in aPRP; (iii) other terminal monosaccharide sites: six in bPRP1, two in bPRP2 and two in bPRP3; (iv) other modifications such as N-terminal pyro-Glu (two in bPRP1, six in bPRP2, eight in bPRP3 and nine in bPRP4); (v) phosphorylation in serine, three in bPRP1, one in bPRP2, one in bPRP3 and one in aPRP1; (vi) bPRP1 (allele S, allele M and variant CP5) and bPRP4 (allele M). In summary, salivary peptidome data analysis allowed the identification of 45 new PRP-modified residues, mainly due to glycosylation, phosphorylation and conversion of Gln to pyro-Glu. Moreover, comparing all subject groups, it was noticed a predominance of N-acetyl hexosamine modification on bPRPs in the Head and Neck Cancer patients.
Vitorino
Rui
R
Department of Chemistry, University of Aveiro, QOPNA, Mass Spectrometry Center, Aveiro, Portugal.
Alves
Renato
R
Barros
António
A
Caseiro
Armando
A
Ferreira
Rita
R
Lobo
Maria Calheiros
MC
Bastos
Ana
A
Duarte
José
J
Carvalho
Davide
D
Santos
Lúcio Lara
LL
Amado
Francisco L
FL
D000595:Amino Acid Sequence; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012463:Saliva / Q000737:chemistry*; D055273:Salivary Proline-Rich Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D020033:Protein Isoforms; D055273:Salivary Proline-Rich Proteins