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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‐Phe43 (statherin SV1), statherin Des‐Thr42,Phe43, statherin Des‐Asp1, statherin Des6–15 (statherin SV2), statherin Des1–9, statherin Des1–10, statherin Des1–13 and P‐B Des1–5. Statherin SV3 (statherin Des6–15, Phe43) 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.