title: Crystal structure analysis of a mutant Escherichia coli thioredoxin in which lysine 36 is replaced by glutamic acid.
abstract: The structure of a mutant Escherichia coli thioredoxin with a glutamic acid substituted for a conserved lysine at position 36 adjacent to the active site has been solved using molecular replacement and refined at 2.0-A resolution to a crystallographic residual of 19.9%. The mutant was crystallized in an orthorhombic space group with one molecule in the asymmetric unit. The structure of the mutant thioredoxin shows overall good agreement with the wild-type E. coli thioredoxin. The root-mean-square deviations for all C alpha s are 0.45 and 0.79 A between the mutant structure and the two molecules in the asymmetric unit of the wild-type crystals. Structural changes are seen in several residues in the active-site region preceding the disulfide. A reverse turn of residues 29-32 changes the conformation from a type I to a type II turn. This change may be related to the loss of a hydrogen bond from Lys-36 to the main-chain carbonyl of residue 30 due to the mutation. The C alpha atom of Trp-31 has moved 1.9 A and the indole ring no longer makes hydrogen bonds to the carboxyl group of Asp-61 but instead participates in a crystal contact. The structural differences seen in the mutant thioredoxin may be influenced by the crystal packing. The substituted Glu-36 makes extensive crystal contacts. The static fluorescence of this mutant thioredoxin has a different pH dependence than the wild type.
authors.affiliation: Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center.
authors.forename: M
authors.initials: M
authors.lastname: Nikkola
authors.forename: F K
authors.initials: FK
authors.lastname: Gleason
authors.forename: J A
authors.initials: JA
authors.lastname: Fuchs
authors.forename: H
authors.initials: H
authors.lastname: Eklund
mesh_terms: D001665:Binding Sites; D003300:Copper / Q000378:metabolism; D003460:Crystallization; D004220:Disulfides / Q000737:chemistry; D004355:Drug Stability; D004926:Escherichia coli / Q000737:chemistry*; D005971:Glutamates; D018698:Glutamic Acid; D006860:Hydrogen Bonding; D008239:Lysine; D015394:Molecular Structure; D016296:Mutagenesis; D011487:Protein Conformation; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013879:Thioredoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D004220:Disulfides; D005971:Glutamates; D012997:Solvents; D018698:Glutamic Acid; D013879:Thioredoxins; D003300:Copper; D008239:Lysine