Principal Investigator_M.Takayama
Analysis of post-translational modifi cation using laser desorption/ionization mass spectrometry
Mitsuo Takayama
Professor, Mass Spectrometry
researchmap
Our Aim
Our aim is to identify post-translational functional groups present on proteins/peptides and identify the specifi c site(s) of the group(s) using matrix-assisted laser desorption/ ionization mass spectrometry (MALDI-TOF MS).
Background
Post-translational modifications of proteins varies signifi cantly between proteins because of the diversity and number of functional groups available for modification. There are a number of challenges that need to be solved for accurately determining the mass of proteins by mass spectrometry, e.g., irregular ion yields of peptides obtained following enzymatic digestion and specifi c cleavage of the peptide backbone. For the analysis of modifi ed proteins/peptides, information about the relationship between ion yield and peptide structure, as well as a suitable method for the specific cleavage at the peptide backbone without degradation of side-chains and functional groups are required.
Research Overview
We will clarify the relationship(s) between ion yield and peptide structure in MALDI and electrospray ionization (ESI) methods. The development of a MALDI method for the specifi c cleavage of the peptide backbone will be attained using matrix materials that have both MALDI matrix and hydrogen transfer reagent functions.
Achievements
Currently, we have obtained the following results:
1. The total ion yield Ji of the peptides can be expressed as the product of the ionization effi ciency I and the rate of vaporization Jv.
2. N-Terminal arginine (R) enhances the ion yield compared to R-free peptides in both the positive and negative ion modes, whereas the presence of a C-terminal R residue decreases the ion yield. The presence of phenylalanine enhances the ion yields in both the positive and negative ion modes. Phosphorylated peptides give rise to a reduced ion yield when compared to the non-phosphorylated peptides in both the positive and negative ion modes. The results obtained are useful for understanding the signal abundance in the peptide-mass fi ngerprints.
3. We have developed new matrix materials for MALDI-TOF MS that enable the N?Cα and Cα?C bonds on the peptide backbone to be specifically cleaved.