Cis-trans signatures of proline-containing tryptic peptides in the gas phase

High-resolution ion mobility/time-of-flight techniques were used to measure collision cross sections for 968 tryptic digest peptide ions obtained from digestion of common proteins. Here, we report a mobility signature that aids in identifying proline-containing peptides containing 4-10 residues. Of 129 peptides (< or = 10 residues in length) in the database that contain proline residues, 57% show multiple resolved features in the ion mobility distribution for at least one of the [M + H]+ or [M + 2H]2+ ions. These multiple features are attributed to different conformations that arise from populations of cis and trans forms of proline. The number of resolved peaks in the ion mobility distribution appears to be correlated with the peptide ion charge state and the number of proline residues in the peptide.