Title : Finding new posttranslational modifications in salivary
proline-rich
proteins
Abstract :
- 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 a PRP
- 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 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 b PRPs in the Head and Neck Cancer patients