Detection in human saliva of different statherin and P-B fragments and derivatives

Statherin is a multifunctional polypeptide specific of human saliva involved in oral calcium homeostasis, phosphate buffering and formation of protein networks. Salivary P-B peptide is usually included into the basic proline-rich protein family but it shows some similarities with statherin and its specific biological role is still undefined. In this study, various fragments and derivatives of statherin and P-B peptide were consistently detected by RP-HPLC ESI-IT MS in 23 samples of human saliva. They were: statherin mono- and non-phosphorylated, statherin Des-Phe(43) (statherin SV1), statherin Des-Thr(42),Phe(43), statherin Des-Asp(1), statherin Des(6-15) (statherin SV2), statherin Des(1-9), statherin Des(1-10), statherin Des(1-13) and P-B Des(1-5). Statherin SV3 (statherin Des(6-15), Phe(43)) was detected only in one sample. Identity of the fragments was confirmed either by MS/MS experiments or by enzymatic digestion or by Edman sequencing. Detection of the fragments suggests that statherin and P-B peptide are submitted to post-translational proteolytic cleavages that are common to other classes of salivary proteins.