Two‐dimensional 1H NMR studies of Ca(II)‐binding site in proteins using paramagnetic lanthanides(III) as probes and Yb(III)‐substituted bovine α‐lactalbumin as an example

Substitution of Yb3+ for the Ca2+ in bovine α‐lactalbumin affords a derivative that gives rise to several isotropically shifted 1H NMR signals in the range 80 to − 35 ppm in D2O. Despite the broadness of the isotropically shifted features, cross signals in both NOESY and COSY spectra have been detected. Several Asp residues in the metal‐binding loop can be recognized in the 2D 1H NMR spectra of this derivative, showing cross signals among the protons of a CβH2CαH moiety. This paper reports 2D 1H NMR studies of a paramagnetic lanthanide(III)‐substituted Ca2+−containing protein that may serve as a model for future NMR studies of other biochemically significant Ca2+ proteins.