MASS-SPECTROMETRIC STUDIES ON NONCOVALENT DIMERS OF LEUCINE-ZIPPER PEPTIDES

The leucine zipper, found in several DNA-binding proteins, represents a motif for noncovalent dimerization to enhance DNA binding. Solution dimerization of the leucine zipper peptides GCN4-p1 and N16V is confirmed here by on-line, size-exclusion liquid chromatography-ion spray mass spectrometry. Tandem mass spectrometry studies indicate that dimer ions also exist in the gas phase. High-resolution trapped-ion studies show that these gaseous dimers are stable for at least minutes. In qualitative agreement with their behavior in aqueous solution, N16V has a greater tendency to form dimers than does GCN4-p1, which unexpectedly forms a noncovalent heterodimer with an impurity.