title: New crystal structures of human glutathione transferase A1-1 shed light on glutathione binding and the conformation of the C-terminal helix.
abstract: Human glutathione transferase A1-1 is a well studied enzyme, but despite a wealth of structural and biochemical data a number of aspects of its catalytic function are still poorly understood. Here, five new crystal structures of this enzyme are described that provide several insights. Firstly, the structure of a complex of the wild-type human enzyme with glutathione was determined for the first time at 2.0 angstroms resolution. This reveals that glutathione binds in the G site in a very similar fashion as the glutathione portion of substrate analogues in other structures and also that glutathione binding alone is sufficient to stabilize the C-terminal helix of the protein. Secondly, we have studied the complex with a decarboxylated glutathione conjugate that is known to dramatically decrease the activity of the enzyme. The T68E mutant of human glutathione transferase A1-1 recovers some of the activity that is lost with the decarboxylated glutathione, but our structures of this mutant show that none of the earlier explanations of this phenomenon are likely to be correct. Thirdly, and serendipitously, the apo structures also reveal the conformation of the crucial C-terminal region that is disordered in all previous apo structures. The C-terminal region can adopt an ordered helix-like structure even in the apo state, but shows a strong tendency to unwind. Different conformations of the C-terminal regions were observed in the apo states of the two monomers, which suggests that cooperativity could play a role in the activity of the enzyme.
authors.affiliation: Department of Cell and Molecular Biology, Uppsala University, Biomedical Centre, Box 596, SE-751 24 Uppsala, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Grahn
authors.forename: Marian
authors.initials: M
authors.lastname: Novotny
authors.forename: Emma
authors.initials: E
authors.lastname: Jakobsson
authors.forename: Ann
authors.initials: A
authors.lastname: Gustafsson
authors.forename: Leif
authors.initials: L
authors.lastname: Grehn
authors.forename: Birgit
authors.initials: B
authors.lastname: Olin
authors.forename: Dennis
authors.initials: D
authors.lastname: Madsen
authors.forename: Mårten
authors.initials: M
authors.lastname: Wahlberg
authors.forename: Bengt
authors.initials: B
authors.lastname: Mannervik
authors.forename: Gerard J
authors.initials: GJ
authors.lastname: Kleywegt
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism*; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics*; D017434:Protein Structure, Tertiary; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D007527:Isoenzymes; D012997:Solvents; D014867:Water; D005982:Glutathione Transferase; C119995:glutathione S-transferase alpha; D005978:Glutathione