Solution structure of the carboxyl terminus of a human class Mu glutathione S-transferase: NMR assignment strategies in large proteins

Strategies to obtain the NMR assignments for the HN, N, CO, Calpha and Cbeta resonance frequencies for the human class mu glutathione-S-transferase GSTM2-2 are reported. These assignments were obtained with deuterated protein using a combination of scalar and dipolar connectivities and various specific labeling schemes. The large size of this protein (55 kDa, homodimer) necessitated the development of a novel pulse sequence and specific labeling strategies. These aided in the identification of residue type and were essential components in determining sequence specific assignments. These assignments were utilized in this study to characterize the structure and dynamics of the carboxy-terminal residues in the unliganded protein. Previous crystallographic studies of this enzyme in complex with glutathione suggested that this region may be disordered, and that this disorder may be essential for catalysis. Furthermore, in the related class alpha protein extensive changes in conformation of the C terminus are observed upon ligand binding. On the basis of the results presented here, the time-averaged conformation of the carboxyl terminus of unliganded GSTM2-2 is similar to that seen in the crystal structure. NOE patterns and 1H-15N heteronuclear nuclear Overhauser enhancements suggest that this region of the enzyme does not undergo motion on a rapid time scale.