THE INFLUENCE OF A SCALAR-COUPLED DEUTERIUM UPON THE RELAXATION OF A N-15 NUCLEUS AND ITS POSSIBLE EXPLOITATION AS A PROBE FOR SIDE-CHAIN INTERACTIONS IN PROTEINS

The magnitude of the quadrupole coupling constant (e(2)Qq/(h) over bar ) of a deuteron is a good probe for hydrogen bonding. In protein struc tures, hydrogen-bonding interactions between side chains, between side chains and ligands, and between side chains and solvent are frequentl y found. An experiment that detects, via scalar coupling, the influenc e of a deuteron on the N-15 nucleus of asparagine or glutamine side ch ains is presented. The experiment depends upon the resolution of the ( 1) Delta(15)N(D) isotope shifts that allow the various isotopomers and isotopologues to be distinguished when N-15-labeled samples are disso lved in solvent mixtures of H2O/D2O. N-15 lineshapes with theoretical simulations that provide estimates for the H-2 quadrupole coupling con stants are presented. The influence of N-15-H-2 dipolar-quadrupole cro ss correlation and the resulting small frequency shifts in the N-15 mu ltiplet are resolved in some of the spectra. The experimental data are provided using the free amino acids asparagine and glutamine for whic h the side chains were isotopically enriched in N-15 and the recombina nt pair of modules, fibronectin type 1 and epidermal growth factor, (F 1-G) of tissue plasminogen activator, which were uniformly isotopicall y enriched in N-15. (C) 1997 Academic Press.