Proton NMR measurements of bacteriophage T4 lysozyme aided by super(15)N isotopic labeling: Structural and dynamic studies of larger proteins

A strategy for resolution and assignment of single proton resonances in proteins of molecular mass up to at least 40 kDa is presented. This approach is based on super(15)N (or super(13)C) labeling of selected residues in a protein. The resonances from protons directly bonded to labeled atoms are detected in a two-dimensional super(1)H- super(15)N (or super(13)C) spectrum. The nuclear Overhauser effects from isotopically tagged protons are selectively observed in one-dimensional isotope-directed measurements. The authors have observed approximately 160 resonances from super(15)N-bonded protons in the backbone and sidechains of uniformly super(15)N-labeled T4 lysozyme (molecular mass = 18.7 kDa).