Research

One goal of our research is to develop mass spectrometric methods to understand interactions between proteins and ligands. To this end, we recently introduced PLIMSTEX (Protein Ligand Interaction by Mass Spectrometry, Titration and H/D Exchange). The accompanying figure shows an example; namely, the titration of fatty acid binding protein (structure of left) with the fatty-acid ligand, potassium oleate, to give a complex (on the right) that now contains the fatty-acid anion. The solid line is computed from a model that gives the equilibrium constant for the interaction: (2.6 ± 0.6) x 10⁶ M^-1, which agrees with a literature value of 3.0 x 10⁶. We think this approach will be important in biophysics and in drug discovery.

A related, second goal is to investigate the gas-phase chemistry of oligodeoxynucleotides. We use tandem MS to explore fragmentation mechanisms, interactions with DNA-binding drugs, and folding of aptamers. We also wish to apply PLIMSTEX to DNA/protein interactions.

A third goal is the development of Fourier transform MS. We design new cells, high-pressure events, and methods for ion stopping to overcome problems of detecting high-mass biomolecules, a development that will be important in proteomics. We also wish to improve accurate mass measurement and to study gas-phase reactions of ions with radicals. Four instruments, two of which are new with 7-tesla magnets, play vital roles in this research.

The laboratory is one of five nationwide MS labs that is supported by the National Center for Research Resources. Under the aegis of this center, students also participate in collaborative research in cancer (with E. Cavalieri and J. Taylor) and immunology (E. Unanue).

Selected Publications

• R. K. Chitta and M. L. Gross, ÒElectrospray ionization-mass spectrometry and tandem mass spectrometry reveal self-association and metal-ion binding of hydrophobic peptides: A study of the gramicidin dimer, Biophysical Journal, 86, 473 (2004).
• A. Suri, J.J. Walters, O. Kanagawa, M.L. Gross, and E.R. Unanue, "Specificity of peptide selection by antigen-presenting cells homozygous or heterozygous for expression of class II MHC molecules: The lack of competition," Proc. Nat. Acad. Sci. USA, 100, 5330 (2003).
• M.M.Zhu, D.L. Rempel, Z. Du, and M.L. Gross, "Quantification of protein-ligand interactions by mass spectrometry, titration, and H/D exchange: PLIMSTEX," J. Am. Chem. Soc., 125, 5252 (2003).
• M. Vairamani and M.L. Gross, "G-Quadruplex formation of thrombin-binding aptamer detected by electrospray ionization mass spectrometry," J. Am. Chem. Soc., 125, 42 (2003).
• M.M. Zhu, D.L. Rempel, J. Zhao, D.E. Giblin, and M.L. Gross, "Probing Ca²⁺-induced conformational changes in porcine calmodulin by H/D exchange and ESI-MS: effect of cations and ionic strength," Biochemistry, 42, 15388 (2003).