Infection by HIV-1 requires protein-protein interactions involving gp120, CD4 and CCR5. We have previously demonstrated that the transferred nuclear Overhauser effect (TRNOE), in combination with asymmetric deuteration of a protein and a peptide ligand can be used to detect intermolecular interactions in large protein complexes with molecular weights up to ~ 100 kDa. Here, using this approach, we reveal interactions between tyrosine residues of a 27-residue peptide corresponding to the N-terminal segment of the CCR5 chemokine receptor, and a dimeric extended core YU 2 gp120 envelope protein of HIV-1 complexed with a CD4-mimic miniprotein. The TRNOE crosspeaks in the ternary complex were assigned to the specific Tyr protons in the CCR5 peptide and to methyl protons of isoleucine, leucine and/or valine residues of gp120. Site directed mutagenesis combined with selective deuteration and TRNOE resulted in the first discernment by a biophysical method of specific pairwise interactions between gp120 residues in the bridging sheet of gp120 and the N-terminus of CCR5.,© 2018 Federation of European Biochemical Societies.