N-Terminal Acetylation Characterization of Tumor Protein D52 by Nano Electrospray Ionization Tandem Mass Spectrometry

M1 mouse acute myeloid leukemia cells were induced to differentiate to huge cells (differentiation into macrophage like cells) after 24 hours by rhIL-6. Using two-dimensional gel analysis, spot A was found to be over expressed at one day after induction and maintained their high levels till fourth day. The spot was subjected to tryptic digestion and then analyzed using PMF of matrix assisted desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) and nanoelectrospray ionization tandem mass spectrometry. Both analyses indicated this to be tumor protein D52. During nano ESI-MS/MS analysis, three peptides were sequenced and the database search result of Mascot MS/MS ion search showed that two peptides matched tumor protein D52 and the other peptide with m/z 1188.66 did not match any protein. Sequence analysis of the MS/MS spectrum revealed that the peptide corresponds to the N-terminal peptide (1–10) of tumor protein D52 with the first methionine acetylated. The sequence of this N-terminal peptide is MDRGEQGLLK. The result matches the previous knowledge of N-acetylation rules in eukaryotes, i.e. the N-terminal methionine is found to be predominantly acetylated when followed by either Asp or Glu. To our knowledge, no report has been published about the N-terminal acetylation of tumor protein 52 till date. The exact role of this modification needs to be studied further.