Research - Noncovalent Interactions

Studies of noncovalently-bound protein-protein and protein-ligand interactions


Protein-protein and protein-ligand interactions are involved in most biological machineries. Characterization of these noncovalent interactions using mass spectrometry has great advantages over other technologies because of high sensitivity and potential to provide stoichiometry and structure information for protein complexes.

ESI-MS (ElectroSpray Ionization Mass Spectrometry)

ESI-MS investigations of noncovalently-bound complexes are interesting because of their relevance to solution biochemistry. ESI is a gentle ionization method, and when it is coupled with highly sensitive mass spectomery, ESI-MS is well suited for studying noncovalent interactions in protein complexes. In the Loo lab, we are using ESI-MS to study α-synuclein and spermine interaction, a Parkinson's disease-related protein-ligand system and nucleotide bound proteins.

GEMMA (Gas-Phase Electrophoretic Mobility Molecular Analysis)

Methods to study large protein complexes expediently are limited. There is a size limit to what can be studied by NMR and x-ray crystallography. For ESI-MS of very large protein complexes or mixtures, multiple charging can lead to difficult to interpret mass spectra. Using ESI ion mobility analysis (GEMMA/macro IMS), particles representing a range of sizes are charge-reduced to singly charged complexes and separated by their electrophoretic mobility in air.


Faller M, Matsunaga M, Yin S, Loo JA, and Guo F. Heme is involved in microRNA processing. Nature Struct Mol Biol 2007; 14: 23-29. (cover article)

Xie Y, Zhang J, Yin S, and Loo JA. Top-Down ESI-ECD-FT-ICR Mass Spectrometry Localizes Noncovalent Protein-Ligand Binding Sites. J Am Chem Soc 2006; 128: 14432-14433.

Loo JA, Berhane BT, Kaddis CS, Wooding KM, Xie Y, Kaufman SL, and Chernushevich IV. Electrospray Ionization Mass Spectrometry and Ion Mobility Analysis of the 20S Proteasome Complex. J Am Soc Mass Spectrom 2005; 16: 998-1008.