J-multiplied HSQC (MJ-HSQC):: A new method for measuring 3J(HNHα) couplings in 15N-labeled proteins

A new method for the measurement of homonuclear (3)J(HNHalpha) coupling constants in N-15-labeled small proteins is described. The method is based on a modified sensitivity enhanced HSQC experiment, where the (3)J(HNHalpha) couplings are multiplied in the f(1)-dimension. The J-multiplication of homonuclear (3)J(HNHalpha) couplings is based on simultaneous incrementation of N-15 chemical shift and homonuclear coupling evolution periods, The time increment for the homonuclear coupling evolution period is chosen to be a suitable multiple (2N x t(1)) of the corresponding increment for N-15-shift evolution. This results in the splitting of the HSQC correlation in the f(1)-dimension by 2N x (3)J(HNHalpha), Because the pulse sequence has good sensitivity and water suppression properties, it is particularly useful for natural abundance samples. (C) 1999 Academic Press.