Nuclear magnetic resonance analysis of Gd3+-induced perturbations in thymopoietin 32-36: a study of amide and aromatic proton resonances

The Gd³⁺-induced perturbations in the NMR spectra of a cell differentiating peptide fragment, ArgLysAspValTyr (TP5), have been examined. This pentapeptide fragment retains the selective T-cell differentiating activity of its parent polypeptide thymic hormone, thymopoietin. The observed relaxation enhancements induced by Gd³⁺ have been analyzed to determine the relative and absolute amide and aromatic proton-Gd³⁺ distances. The data are compatible with a bidentate model, in which both the aspartyl and tyrosyl carboxylates bind the metal ion simultaneously in a chelate fashion, being the dominant conformer. From these studies a picture of the conformation of Ln³⁺ complexes of TP5 begins to emerge.