Scientific News

Seattle, WA (U.S.A.) --- An exciting scientific breakthrough into protein conformation study through a newly-developed laser spray mass spectrometry was reported by Dr. Xianggguo Shi at Yokohama University (Japan) and coworkers last month.

Laser spray, developed by Dr. Shi’s collaborator Prof. Hiraoka at Yamanshi University, is a hybrid of three basic techniques for the generation of gaseous ions from the condensed phase. Laser spray mass spectrometry can faithfully reflect the solution-phase characteristics of biomolecules. Dr. Shi and coworkers have successfully applied laser spray to evaluate the binding affinities of protein-DNA and drug-DNA complexes, which is a topic of importance and challenge in biophysics and medical chemistry.

One of the advantages of laser spray in the analysis of biomolecules is its convenience. Laser spray provides information on the stability of biomolecules instantly just by tuning the laser power. In this recent work, published in the April 2008 issue of Rapid Commun Mass Spectrom, Dr. Shi investigated whether laser spray could be employed to analyze the thermal stability and folding transitions of proteins quantitatively. Horse heart cytochrome c (cyt c, Protein Data Bank (PDB) ID: 1HRS) is a small heme protein, whose molecular weight is 12,365, with 104 amino acid residues and plays an important role in transferring electrons in the respiratory chain. In the reported study, they used cyt c as a model protein to establish the methodology in the conformational study. The stability of horse heart cytochrome c and bovine ubiquitin was evaluated by laser spray and compared in this study.

Researchers found that laser spray mass spectrometry enables much faster and more convenient monitoring of conformational changes of cyt c than does conventional electrospray ionization mass spectrometry (ESI-MS). Laser spray mass spectra of cyt c at various pH were obtained at different levels of laser power. Bimodal charge-state distributions of the protein were observed in laser spray mass spectra, indicating the two-state model of structural change; the lower charges correspond to the folded state, the higher charges to the unfolded state. The results from laser spray mass spectrometry correlated well with circular dichroism (CD) experiments under relatively acidic conditions, which destabilize the protein. The thermal stabilities of ubiquitin and cyt c prepared in solutions at the same pH were also easily differentiated by corresponding laser power. Their exciting studies indicate that laser spray mass spectrometry could be a versatile method for rapid evaluation of the thermal stability of proteins, and for observation of conformational changes by a simple tuning of the laser power.

ESI-MS, developed by John B. Fenn, was used to identify and analyze biological macromolecules in the past decade. Dr. Fenn was awarded the Nobel Prize in Chemistry in 2002 for the contribution in the development of ESI-MS in the biological application. Laser spray mass spectrometry was developed based on ESI-MS, yet Dr. Shi’s groundbreaking research strongly supports that laser spray offers greater advantage than does ESI-MS in the study of the binding affinity of biomolecular complexes and conformational study of proteins. More importantly, laser spray could reflect faithfully the biophysical characteristics of biomolecules, such as binding affinities. These discoveries confirmed that laser spray is a new powerful method to screen drug candidates such as antibiotics and anticancer drugs. This new mass spectrometry technique may win the Nobel Prize for its inventor and his coworkers in the future. We look forward to the new and exciting scientific discoveries from the further development and application of laser spray.