Measurement of relaxation rates of N-H and H-alpha backbone protons in proteins with tailored initial conditions

Several methods are presented for the selective determination of spin-latti ce and spin-spin relaxation rates of backbone protons in labeled proteins. The relaxation rates of amide protons in N-15 labeled proteins can be measu red by using two-way selective cross-polarization (SCP). The measurement of H-alpha relaxation rates can be achieved by combining this method with hom onuclear Hartmann-Hahn transfer using doubly selective irradiation. Various schemes for selective or nonselective inversion of the longitudinal proton magnetization lead to different initial recovery rates. The methods have b een applied to lysine K6 in N-15-labeled human ubiquitin and to leucine L5 in N-15- and C-13-labeled octapeptide YG*G*F*LRRI (GFL) in which the marked residues are N-15- and C-13-labeled. (C) 1999 Academic Press.