title: Crystal structure of a NifS-like protein from Thermotoga maritima: implications for iron sulphur cluster assembly.
abstract: NifS-like proteins are ubiquitous, homodimeric, proteins which belong to the alpha-family of pyridoxal-5'-phoshate dependent enzymes. They are proposed to donate elementary sulphur, generated from cysteine, via a cysteinepersulphide intermediate during iron sulphur cluster biosynthesis, an important albeit not well understood process. Here, we report on the crystal structure of a NifS-like protein from the hyperthermophilic bacterium Thermotoga maritima (tmNifS) at 2.0 A resolution. The tmNifS is structured into two domains, the larger bearing the pyridoxal-5'-phosphate-binding active site, the smaller hosting the active site cysteine in the middle of a highly flexible loop, 12 amino acid residues in length. Once charged with sulphur the loop could possibly deliver S(0) directly to regions far remote from the protein. Based on the three-dimensional structures of the native as well as the substrate complexed form and on spectrophotometric results, a mechanism of sulphur activation is proposed. The His99, which stacks on top of the pyridoxal-5'-phosphate co-factor, is assigned a crucial role during the catalytic cycle by acting as an acid-base catalyst and is believed to have a pK(a) value depending on the co-factor redox state.
authors.affiliation: Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, Martinsried, D-82152, Germany.
authors.forename: J T
authors.initials: JT
authors.lastname: Kaiser
authors.forename: T
authors.initials: T
authors.lastname: Clausen
authors.forename: G P
authors.initials: GP
authors.lastname: Bourenkow
authors.forename: H D
authors.initials: HD
authors.lastname: Bartunik
authors.forename: S
authors.initials: S
authors.lastname: Steinbacher
authors.forename: R
authors.initials: R
authors.lastname: Huber
mesh_terms: D000501:Allylglycine / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D002384:Catalysis; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism; D019281:Dimerization; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008190:Lyases / Q000737:chemistry; D008239:Lysine / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017433:Protein Structure, Secondary; D011732:Pyridoxal Phosphate / Q000378:metabolism; D012645:Selenomethionine / Q000378:metabolism; D013053:Spectrophotometry; D013455:Sulfur / Q000378:metabolism*; D020124:Thermotoga maritima / Q000737:chemistry* / Q000235:genetics; D000637:Transaminases / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; C080001:nifS protein, Bacteria; D000501:Allylglycine; D006639:Histidine; D011732:Pyridoxal Phosphate; D013455:Sulfur; D012645:Selenomethionine; D000637:Transaminases; C022393:phosphoserine aminotransferase; D008190:Lyases; C019965:cystathionine beta-lyase; D008239:Lysine; D003545:Cysteine