A New Copper Containing MALDI Matrix That Yields High Abundances of [Peptide + Cu]+ Ions

The dinuclear copper complex (α-cyano-4-hydroxycinnamic acid (CHCA) copper salt (CHCA)4Cu2), synthesized by reacting CHCA with copper oxide (CuO), yields increased abundances of [M + xCu − (x−1)H]+ (x = 1–6) ions when used as a matrix for matrix-assisted laser desorption ionization (355 nm Nd:YAG laser). The yield of [M + xCu − (x−1)H]+ (x = 1∼6) ion is much greater than that obtained by mixing peptides with copper salts or directly depositing peptides onto oxidized copper surfaces. The increased ion yields for [M + xCu − (x−1)H]+ facilitate studies of biologically important copper binding peptides. For example, using this matrix we have investigated site-specific copper binding of several peptides using fragmentation chemistry of [M + Cu]+ and [M + 2Cu − H]+ ions. The fragmentation studies reveal interesting insight on Cu binding preferences for basic amino acids. Most notable is the fact that the binding of a single Cu+ ion and two Cu+ ions are quite different, and these differences are explained in terms of intramolecular interactions of the peptide-Cu ionic complex.

Graphical AbstractA Cu-containing MALDI matrix ((CHCA)4Cu2) for gas-phase studies of [M + xCu − (x−1)H]+ ions.Figure optionsDownload full-size imageDownload high-quality image (178 K)Download as PowerPoint slide