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2D [15N, 1H] HSQC for peak dispersion and peak yield assessment
The following peaks are alway visible in [15N, 1H] HSQC:
- 1 peak for each backbone amide except that of the first residue
- 1 peak for each Trp side chain HE1/NE1 group, usually located in the most downfield region.
- 4 peaks for each Asn and Gln side chain - these are ND2/HD21, ND2/HD22 of -CONH2 and -CONHD groups. -CONHD peaks appear due to the exchange with D2O and have distinct chemical shifts due to deuterium isotope effects. Usually CONHD peaks are much weaker and located above the CONH2 peaks.
The following peaks are also sometimes observed in [15N, 1H] HSQC:
- NE/HE of Arg (a few are normally visible in every protein, 15N shift ~90 ppm)
- NH1/HH11, NH1/HH12, NH2/HH21, NH2/HH22 of Arg (rarely visible, usually broad, 15N shift ~70 ppm)
- ND1/HD1 and/or HE2/HE2 of His (rarely visible, 15N shifts vary greatly, can be mistaken for Trp)