Voronina, LiudmilaMasson, AntoineKamrath, MikeSchubert, FranziskaClemmer, David E.Baldauf, CarstenRizzo, Thomas R.2016-07-052016-07-052016-07-05201610.1021/jacs.6b04550https://infoscience.epfl.ch/handle/20.500.14299/127018WOS:000380730000042The dynamic nature of intrinsically disordered peptides makes them a challenge to characterize by solution-phase techniques. In order to gain insight into the relation between the disordered state and the environment, we explore the conformational space of the N-terminal 1-5 fragment of bradykinin (BK[1-5]2+) in the gas phase by combining drift tube ion mobility, cold-ion spectroscopy, and first principles simulations. The ion-mobility distribution of BK[1-5]2+ consists of two well-separated peaks. We demonstrate that the conformations within the peak with larger cross-section are kinetically trapped, while the more compact peak contains low-energy structures. This is a result of cis-trans isomerization of the two prolyl-peptide bonds in BK[1-5]2+. Density-functional theory calculations reveal that the compact structures have two very different geometries with cis-trans and trans-cis backbone conformations. Using the experimental CCSs to guide the conformational search, we find that the kinetically trapped species have a trans-trans configuration. This is consistent with NMR measurements performed in a solution, which show that 82% of the molecules adopt a trans-trans configuration and behave as a random coil.peptidesspectroscopyion mobilitytext::journal::journal article::research article