A J(CH)-modulated 2D (HACACO)NH pulse scheme for quantitative measurement of C-13(alpha)-H-1(alpha) couplings in N-15, C-13-labeled proteins

A triple-resonance pulse sequence is presented for the quantitative measure ment of H-1(alpha)-C-13(alpha) single-bond couplings in N-15, C-13 uniforml y labeled proteins. This (1)J(CH)-modulated (HACACO)NH experiment yields H- 1(N)-N-15-correlated 2D spectra in which the amplitude of each peak is modu lated by the H-1(alpha)-C-13(alpha) J coupling of the preceding residue, (i - 1). The experiment is demonstrated on a 1.0 mM sample of Rho130, the 15- kDa RNA binding domain of E. coli Rho factor. The average error in the meas ured coupling constants was less than 0.8%. This sequence allows the measur ement of the (1)J(CH) couplings from a proton-nitrogen HSQC without the nee d for assigning the H-alpha and C-alpha resonances. (C) 1999 Academic Press .