[13C]-constant-time [15N,1H]-TROSY-HNCA for sequential assignments of large proteins.

The greatly improved sensitivity resulting from the use of TROSY during 15N evolution and amide proton acquisition enables the recording of HNCA spectra of large proteins with constant-time 13C alpha evolution. In [13C]-ct-[15N,1H]-TROSY-HNCA experiments with a 2H/13C/15N-labeled 110 kDa protein, 7,8-dihydroneopterin aldolase from Staphylococcus aureus, nearly all correlation peaks seen in the [15N,1H]-TROSY-HNCA spectrum were also detected. The improved resolution in the 13C dimension then enabled a significant number of sequential assignments that could not be obtained with [15N,1H]-TROSY-HNCA without [13C]-constant-time period.