Optimization of MALDI-TOF MS methods for the analysis of peptide beads selected from the screening of one bead-one peptide combinatorial libraries

MARTINEZ CERÓN, M. C.; GIUDICESSI, S. L.; MARANI, M. M.; CÔTE, S.; ERRA-BALSELLS, R.; ALBERICIO, F.; CAMPERI, S. A.; CASCONE, O.

Villa Carlos Paz

Congreso; XLIV Reunion Annual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2008

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

One bead-one peptide combinatorial libraries, an important tool for new ligand identification, involves the synthesis of millions of peptides on beads so that each bead displays only one peptide entity. The library is screened against specific targets. Positive beads are isolated and analyzed. We reported a rapid and inexpensive method based on MALDI-TOF analysis. Contaminants, matrix clusters and metal ion adducts interfere with peptide ionization and mass spectrum interpretation. In this work we analyzed different strategies to improve MALDI spectra. We replaced the guanidine used for bead washing before MALDI analysis with a mixture of acetonitrile (ACN), acetic acid (AcOH) and H2O. Removal of guanidine as contaminant improved matrix crystallization. We optimized peptide-bead cleavage and peptide elution: beads were placed into microtubes in a desiccator together with a flask containing NH4OH. Cleaved peptides were eluted from the beads with 20 μl of AcOH- ACN-H2O and 0,5 μl of sample was loaded onto the sample plate. Elution of peptides in microtubes instead of placing the bead in the sample plate increased sample aliquots in case spectrum had to be repeated. Among the matrices analysed, -Cyano-4-hydroxycinnamic acid induced higher peptide ionization. To minimize clusters and adducts, we added serine or NH4H2PO4, what resulted in the increase of signal-to-noise ratio.