(a) 2D (1H,13C)-CT-HSQC of U-[13C, 15N]-GGC. Location of different methyl groups is highlighted by coloured ellipses, two ellipses are shown for racemic methyl groups of Leu and Val. 2D (1H,13C)-HMQC of (b) U-[D, 15N],(Ile-δ1)-[13CH3], (c) U-[D,15N],(Ala-β, Leu/ValproS)-[13CH3] or (d) U-[D, 15N],(Ala-β)-[13CH3]-(Leu/Val)-[13CH3,12CD3]-labelled GGC.