Poster Presentation 10th Australian Peptide Conference 2013

General mechanism of matrix-assisted laser desorption/ionization in-source decay mass spectrometry: Toward a novel method for De Novo sequencing of peptides and proteins (#137)

Daiki Asakawa 1 2 , Nicolas Smargiasso 1 , Loic Quinton 1 , Edwin De Pauw
  1. University of Liege, Liege, Belgium
  2. Osaka MCH, Izumi, Osaka, Japan
MALDI in-source decay (MALDI-ISD) is a fragmentation that occurs in the MALDI source. It has already been successfully used for the de novo sequencing of peptides and proteins, including the localization of post-translational modifications. MALDI-ISD involves the hydrogen attachment to peptides, leading the N–Cα bond cleavage. The source of the hydrogen radical involved in MALDI-ISD was investigated by Takayama using deuterium-labeled peptide and/or matrix. The result clearly shows that MALDI-ISD is initiated by the hydrogen transfer from the matrix to the peptide. However, the mechanism of fragmentation that follows this transfer is not fully understood.During our investigations, we observed that the formation of ISD ions was suppressed by using ionic liquid and amorphous structure of matrix whereas strong signal were observed on sharp crystals. This seems to indicate that the initial step of MALDI-ISD forming hydrogen-abundant peptide radical mainly occurs on the matrix crystal during the dissipation of the laser energy. Resulting hydrogen-abundant peptide radical fragments into c/z• fragments pair by radical-induced N–Cα bond cleavage located on the right side of radical site. Subsequently, z• radicals evolve by reacting with a matrix molecule or by losing their side-chain. These two reactions competitively occur and are controlled by the collision rate in MALDI plume. This work led to new insights in the hydrogen-abundant radical formation, N–Cα bond cleavage and further radical reaction processes during MALDI-ISD that will be helpful to interpret MALDI-ISD spectra of peptides and proteins.