Asparaginyl endopeptidase mapping of proteins with subsequent matrix-assisted laser desorption/ionization mass spectrometry.

A matrix-assisted laser desorption/ionization (MALDI) mass spectrometric mapping strategy for the identification and characterization of isolated and purified proteins is described. The method, which employs the combined usage of a new site-specific enzyme Asparaginyl endopeptidase (Asn-EP) for proteolysis, and MALDI for subsequent mass analysis, is capable of rapidly and sensitively examining the components of complex mixtures without any chromatographic or electrophoretic separation steps. Subpicomole sample quantities typically suffice to permit the confirmation of deduced primary structures and/or the identification of possible post-translational modifications. The data obtained should also prove useful for mass matching and sequence homology searching of computerised protein sequence data bases of known proteins.