Mass Spec Maps Disordered Proteins

Amide hydrogen/deuterium exchange mass spectrometry (H/D-MS), a technique that reveals which protein residues are flexible or exposed to solvent, is an effective tool for mapping the unstructured regions of intrinsically disordered proteins (IDPs) and their transitions to well-folded forms in complexes, researchers report (Biochemistry, DOI: 10.1021/bi200875p). For measuring H/D exchange, mass spectrometry requires less material than other methods such as nuclear magnetic resonance. IDPs are floppy proteins that lack a structured conformation. They often perform functions that require protein-protein interactions, such as signaling. David D. Weis and coworkers at the University of Kansas used H/D-MS to monitor the interaction of two well-characterized IDPs—an unstructured protein called ACTR and a molten globular protein called CBP—as they form a well-folded complex. Most parts of ACTR exchange at rates consistent with unstructured proteins, but residual structure was detected in the parts that form helices in the complex. In contrast, CBP is moderately protected against exchange along its entire length, indicating that it is transiently unstructured. When the two proteins come together, H/D-MS can be used to identify regions involved in binding and folding of the complex.