Transferred cross-correlated relaxation complements transferred NOE: Structure of an IL-4R-derived peptide bound to STAT-6

A new NMR method is proposed which enables the measurement of projection an gles in the bound conformation of a weakly binding ligand complexed to its receptor. The method is based on the cross-correlated relaxation mechanism. In analogy to the transferred NOE experiment (trNOE), cross-correlated rel axation can be transferred and measured at the resonances of the free ligan d (trCCR), provided the k(off) rate is within the time scale of the experim ent. The concept is validated by the structure determination of an interleu kin-4 (IL-4) receptor-derived partially C-13- and N-15-labeled phosphotyros ine peptide ligated to STAT-6. Distances have been obtained by trNOE experi ments, and the torsion angle Pro(psi) has been determined using trCCR, meas uring either cross-correlated H-N-N/H-alpha-C-alpha dipole-dipole relaxatio n or cross-correlated H-alpha-C-alpha dipole/CO chemical shift anisotropy r elaxation. The resulting structure has been described.