H(C)CH-COSY and (H)CCH-COSY experiments for 13C-labeled proteins in H2O solution

We present three experiments which serve to identify carbon and proton sidechain resonances in 13C-labeled proteins. The first is an improvement on the previously published H(C)CH-COSY experiment and comprises the application of gradients for coherence selection and a reduction in the phase cycle. The second experiment is a new (H)CCH-COSY with two carbon dimensions. The (H)CCH-COSY presents several advantages over the H(C)CH-COSY experiment in terms of better sensitivity, improved resolution and easier identification of amino acid spins systems. The third experiment is a 2D proton-edited (H)C(C)H-COSY that allows suppression of methylene resonances. All three HCCH-COSY experiments show good sensitivity and excellent solvent suppression. The 2D version can be acquired in as little as 45 minutes and the 3D versions acquired overnight. The experiments are demonstrated on a 13C-labeled sample of the second PDZ domain from human phosphatase PTP1E in H2O solution.