Effects of Protein-pheromone Complexation on Correlated Chemical Shift Modulations

Major urinary protein (MUP) is a pheromone-carrying protein of the lipocalin family. Previous studies by isothermal titrn. calorimetry (ITC) show that the affinity of MUP for the pheromone 2-methoxy-3-isobutylpyrazine (IBMP) is mainly driven by enthalpy, with a small unfavorable entropic contribution. Entropic terms can be attributed in part to changes in internal motions of the protein upon binding. Slow internal motions can lead to correlated or anti-correlated modulations of the isotropic chem. shifts of carbonyl C' and amide N nuclei. Correlated chem. shift modulations (CSM/CSM) in MUP have been detd. by measuring differences of the transverse relaxation rates of zero- and double-quantum coherences ZQC{C'N} and DQC{C'N}, and by accounting for the effects of correlated fluctuations of dipole-dipole couplings (DD/DD) and chem. shift anisotropies (CSA/CSA). The latter can be predicted from tensor parameters of C' and N nuclei that have been detd. in earlier work. The effects of complexation on slow time-scale protein dynamics can be detd. by comparing the temp. dependence of the relaxation rates of APO-MUP (i.e., without ligand) and HOLO-MUP (i.e., with IBMP as a ligand). [on SciFinder (R)]