Gln-Gly cleavage: Correlation between collision-induced dissociation and biological degradation

Tryptic digestion of the 150-residue human acidic salivary proline-rich pro tein 1 (PRP-1) generated eight peptides, two of which corresponded to the N -terminal 30-residue segment. In each of the other six tryptic peptides, a consensus repeat with the structure PQGPPQQGG was present. A facile Gln-Gly cleavage between the second and the third residues of the repeat was obser ved during collision-induced dissociation experiments. We postulate possibl e mechanisms to account for this reactivity, involving attack on the peptid yl carbonyl group by the Gin sidechain. Significantly, the Gln-Gly cleavage has been shown to be biologically important in the bacterial degradation o f PRPs in saliva, generating bacteria-binding Pro-Gin C-termini. We suggest a Link between the gas-phase chemistry and the biochemical degradation of these molecules. (C) 2001 American Society for Mass Spectrometry.