title: Glutathione induces helical formation in the carboxy terminus of human glutathione transferase A1-1.
abstract: The structure and dynamic properties of the C-terminal region of the human class alpha glutathione transferase A1-1 have been investigated with high-resolution NMR methods. On the basis of crystallographic and fluorescence measurements, this 13-residue segment of the enzyme is presumed to be disordered in the unliganded enzyme. When the product or product analogue is bound, a C-terminal alpha-helix is observed in crystal structures. Conflicting data exists regarding the structure of this region when one of the substrates, glutathione (GSH), is bound. The NMR studies presented here show that in the unliganded protein, this region of the protein samples different conformations, most likely an ensemble of helix-like structures. Addition of either GSH or the conjugate between GSH and ethacrynic acid (EASG) causes this segment to become a stable alpha-helix. In the GSH complex, the ends of this helix exhibit dynamic behavior on both the millisecond and nanosecond time scales. In contrast, there is no evidence of millisecond dynamics in the EASG complex. The ligand-induced ordering of the enzyme reduces the intrinsic affinity of the enzyme for its product, facilitating enzymatic turnover.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Zhan
authors.forename: Gordon S
authors.initials: GS
authors.lastname: Rule
mesh_terms: D000577:Amides / Q000737:chemistry; D000595:Amino Acid Sequence; D004976:Ethacrynic Acid / Q000737:chemistry / Q000494:pharmacology; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism*; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary
chemical_list: D000577:Amides; D007527:Isoenzymes; D008024:Ligands; D005982:Glutathione Transferase; C119995:glutathione S-transferase alpha; D005978:Glutathione; D004976:Ethacrynic Acid; D009584:Nitrogen