Abundant phosphorylation events control the activity of nuclear proteins involved in gene regulation and DNA repair. These occur mostly on disordered regions of proteins, which often contain multiple phosphosites. Comprehensive and quantitative monitoring of phosphorylation reactions is theoretically achievable at a residue‐specific level using 1H‐15N NMR spectroscopy, but is often limited by low signal‐to‐noise at pH>7 and T>293 K. We have developed an improved 13Cα‐13CO correlation NMR experiment that works equally at any pH or temperature, that is, also under conditions at which kinases are active. This allows us to obtain atomic‐resolution information in physiological conditions down to 25 μm. We demonstrate the potential of this approach by monitoring phosphorylation reactions, in the presence of purified kinases or in cell extracts, on a range of previously problematic targets, namely Mdm2, BRCA2, and Oct4.

Intrinsically disordered proteins (IDPs) constitute an important class of biomolecules with high flexibility. Atomic resolution studies for these molecules are essentially limited to NMR spectroscopy, which should be performed under physiological pH and temperature to populate relevant conformational ensembles. In this context, however, fundamental problems arise with established triple resonance NMR experiments: high solvent accessibility of IDPs promotes water-exchange, which disfavors classical amide 1 H-detection, while 13 C-detection suffers from significantly reduced sensitivity. A favorable alternative, the conventional detection of non-exchangeable 1 H so far resulted in broad signals with insufficient resolution and sensitivity. To overcome this we introduce here a selective H,C-correlating pure shift detection scheme, the SHACA-HSQC, using extensive hetero-and homo-nuclear decoupling applicable to aqueous samples (≥ 90% H 2 O) and tested on small molecules and proteins. SHACA-HSQC spectra acquired on IDPs provide uncompromised resolution and sensitivity (up to 5-fold increased S/N compared to the standard 1 H, 13 C-HSQC), as shown for resonance distinction and unambiguous assignment on the disordered transactivation domain of the tumorsuppressor p53, synuclein, and folded ubiquitin. The detection scheme can be implemented in any 1 H-detected triple resonance experiment, but may also form the basis for the detection of isotope-labeled markers in biological studies or compound libraries.