N,N-Dimethylaminopyrene as a fluorescent affinity mass tag for ligand-binding mode analysis.

Elucidation of the binding mode of protein–ligand interactions provides insights for the design of new pharmacological tools and drug leads. Specific labeling of target proteins with chemical probes, in which the ligands are conjugated with reacting and detecting groups, can establish the binding positions of ligands. Label-assisted laser desorption/ionization mass spectrometry (LA-LDI MS) is a promising detection method to selectively detect labeled molecules. However, previous LDI MS tags, such as nitrogen-substituted pyrenes, had problems with low sensitivity and stability. Here we show 6-N,N-dimethylaminopyrene (dmpy) as a versatile mass tag, which was detected at an amount of 0.1 fmol by LA-LDI MS and applicable for MS/MS analysis. By using ligand-dissociation-type dmpy probes and affinity purification with a polystyrene gel, we demonstrated that dmpy-labeled peptides were predominantly detected by MALDI MS. Our dmpy-probe-labeling method might be highly useful for determining the target biomacromolecules of various ligands and their binding sites.