Mapping protein-protein interactions by double-REDOR-filtered magic angle spinning NMR spectroscopy.

REDOR-based experiments with simultaneous H-C and H-N dipolar dephasing are explored for investigating intermolecular protein-protein interfaces in complexes formed by a U-C,N-labeled protein and its natural abundance binding partner. The application of a double-REDOR filter (dREDOR) results in a complete dephasing of proton magnetization in the U-C,N-enriched molecule while the proton magnetization of the unlabeled binding partner is not dephased. This retained proton magnetization is then transferred across the intermolecular interface by H-C or H-N cross polarization, permitting to establish the residues of the U-C,N-labeled protein, which constitute the binding interface. To assign the interface residues, this dREDOR-CPMAS element is incorporated as a building block into C-C correlation experiments. We established the validity of this approach on U-C,N-histidine and on a structurally characterized complex of dynactin's U-C,N-CAP-Gly domain with end-binding protein 1 (EB1). The approach introduced here is broadly applicable to the analysis of intermolecular interfaces when one of the binding partners in a complex cannot be isotopically labeled.