DETECTION AND STRUCTURAL CHARACTERIZATION OF RAS ONCOPROTEIN-INHIBITORS COMPLEXES BY ELECTROSPRAY MASS-SPECTROMETRY

MS based methodology employing electrospray ionization (ESI) is descri bed for the detection of ternary complexes in which SCH 54292 or SCH 5 4341 and GDP are noncovalently bound to oncogenic ras protein. The obs erved molecular weights of 19,816 and 19,570 Da confirmed the presence of noncovalent complexes of ras-GDP-SCH 54292 and ras-GDP-SCH 54341, respectively. We have also performed selective chemical modification o f lysine residues of the ras protein complex followed by enzymatic dig estion and on-line LC-ESI MS peptide mapping to determine protein-drug binding topography. There was a good correlation between nucleotide e xchange inhibition as determined by the enzyme assay and evidence of c omplex formation as determined by MS. (C) 1997 Elsevier Science Ltd.