Multiple Bradykinin States Revealed

The peptide bradykinin adopts at least 10 conformational states in solution, according to ion mobility spectrometry and mass spectrometry measurements (J. Am. Chem. Soc., DOI: 10.1021/ja203895j). Bradykinin is a nine-amino-acid peptide known to be involved in pain and inflammation. Despite extensive interest in bradykinin, its structure has been only partially characterized. Using a combination of ion mobility and mass spectrometry, David E. Clemmer of Indiana University and coworkers analyzed bradykinin across a range of solution compositions typically used with the peptide. Ion mobility separates species on the basis of their shape, whereas mass spectrometry separates them on the basis of their mass-to-charge ratio. The peptide’s gas-phase equilibrium includes three different conformers, but in solution additional conformers are revealed. For example, in a 90:10 mixture of dioxane to water, bradykinin adopts as many as eight conformers. In all, the researchers found 10 different conformers. “Such a large number of coexisting structures explains the inability of traditional methods of characterization such as nuclear magnetic resonance spectroscopy and crystallography to determine detailed structural features for some regions of this peptide,” the researchers write.