Direct measurement of the 15N CSA/dipolar relaxation interference from coupled HSQC spectra.

Here we propose a method for the measurement of the (15)N CSA/dipolar relaxation interference based on direct comparison of the (15)N doublet components observed in a (1)H-coupled (1)H-(15)N HSQC-type spectrum. This allows the determination of the cross-correlation rates with no need for correction factors associated with other methods. The signal overlap problem of coupled HSQC spectra is addressed here by using the IPAP scheme (Ottiger et al., 1998). The approach is applied to the B3 domain of protein G to show that the method provides accurate measurements of the (15)N CSA/dipolar cross-correlation rates.