Mapping the Conformational Landscape of the Cold-Regulated Intrinsically Disordered Protein COR15A

Cold regulated protein 15A (COR15A) is a late embryogenesis abundant (LEA) protein from Arabidopsis thaliana that is expressed in response to low temperatures and dehydration. Here, we use a combination of ion mobility-mass spectrometry (IM-MS) and molecular dynamics (MD) simulations at elevated temperatures for enhanced sampling to explore the conformational landscape of COR15A. The IM-MS data display charge states from +5 to +12, and collision cross section (CCS) distributions indicative of two dominant coexisting conformational families centered on approximately 1200 and 1800 Å2, with subconformers evident. The structures sampled with MD are histogrammed, which provides a pseudo-CCS distribution (pCCS) highly similar to experimental IM-MS data, allowing us to compare with small-angle X-ray scattering-derived structures of COR15A in functional conditions. This approach gives compelling evidence that the experimental gas-phase data correspond to natively accessible states. In contrast to commonly used biophysical approaches, IM-MS permits simultaneous observation of disordered forms as well as conformers populated upon dehydration, allowing insights into dehydration-responsive LEA proteins.