Structural characterization of a new statherin from pig parotid granules

This study describes the identification and structural characterization of Sus scrofa statherin. HPLC-electrospray ionization mass spectrometry analysis on pig parotid secretory granule extracts evidenced a peptide with a molecular mass value of 5381.1 +/- 0.6 Da and its truncated form, devoid of the C-terminal Ala residue, with a molecular mass value of 5310.1 +/- 0.6 Da. The complete sequence of pig statherin gene was determined by sequencing the full-length cDNA obtained by rapid amplification of cDNA ends. The gene is 549 base pairs long and contains an open reading frame of 185 nucleotides, encoding a 42-amino acid secretory polypeptide with a signal peptide of 19 residues. This sequence presents some typical features of the four statherins characterized till now, showing the highest degree of amino acid identity with bovine (57%) and human statherin (39%). Pig statherin is mono-phoshorylated on Ser-3, while primate statherins already characterized are di-phosphorylated on Ser-2 and Ser-3. This difference, probably connected to the Asp-4 -> Glu substitution, suggests the involvement of the Golgi-casein kinase, which strictly recognizes the SX(E/pS) consensus sequence.