De novo sequencing of proteolytic peptides by a combination of C-terminal derivatization and nano-electrospray/collision-induced dissociation mass spectrometry

A series of synthetic peptides (3-15 residues), C-terminally derivatized wi th 4-aminonaphthalenesulfonic acid (ansa), have been analyzed on a hybrid m agnetic sector-orthogonal acceleration time-of-flight tandem mass spectrome ter, fitted with a nano-electrospray (nano-ES) interface. Deprotonated mole cules generated by negative-ion ES were subjected to collision-induced diss ociation (CID) using either methane or xenon as the collision gas, at a col lision energy of 400 eV (laboratory frame of reference). As a consequence o f charge localization on the sulfonate group, only C-terminal fragment ions were formed, presumably by charge-remote fragmentation mechanisms. Interpr etable CID spectra were obtained from fmol amounts of the small peptides (u p to 6 residues), whereas low pmol amounts were required for the larger pep tides. CID spectra were also recorded of derivatized, previously noncharact erised peptides obtained by proteolysis of cytosolic hamster liver aldehyde dehydrogenase. Interpretation of these CID spectra was based on rules esta blished for the fragmentation of the synthetic peptides. This study shows t hat derivatization with ansa may be useful in the de novo sequencing of pep tides. (J Am Soc Mass Spectrom 2000, 11, 673-686) (C) 2000 American Society for Mass Spectrometry.