Abstract
Acetylation of the amino-groups of HIV-p24 proteins with normal acetic anhydride and deuterated acetic anhydride followed by the mass spectrometric peptide mapping was carried out for the evaluation of relative reactivities of lysine residues at varying locations. The mild acetylation by normal acetic anhydride giving partially acetylated (h-Ac) lysine residues was followed by the complete deuteroacetylation to label the unreacted lysine residues with trideuteroacetic groups (d-Ac). The relative reactivities of lysine residues were evaluated based on the ratios of h-Ac/d-Ac observed by electrospray ionization mass spectrometry of unfractionated tryptic digests of acetylated p24. The relative reactivities of four lysine residues (K158>K170≥K 140>K25) showed a correlation with their solvent accessibilities (SA) derived from the tertiary structure of HIV-p24 predicted by computer modeling and X-rar crystallographic analyses. It is shown that the combination of selective chemical modification and mass spectrometric peptide mapping of proteins is useful to probe their tertiary structures derived from X-ray crystallography or NMR spectroscopy.
