title: Identification of a novel archaebacterial thioredoxin: determination of function through structure.
abstract: As part of a high-throughput, structural proteomic project we have used NMR spectroscopy to determine the solution structure and ascertain the function of a previously unknown, conserved protein (MtH895) from the thermophilic archeon Methanobacterium thermoautotrophicum. Our findings indicate that MtH895 contains a central four-stranded beta-sheet core surrounded by two helices on one side and a third on the other. It has an overall fold superficially similar to that of a glutaredoxin. However, detailed analysis of its three-dimensional structure along with molecular docking simulations of its interaction with T7 DNA polymerase (a thioredoxin-specific substrate) and comparisons with other known members of the thioredoxin/glutaredoxin family of proteins strongly suggest that MtH895 is more akin to a thioredoxin. Furthermore, measurement of the pK(a) values of its active site thiols along with direct measurements of the thioredoxin/glutaredoxin activity has confirmed that MtH895 is, indeed, a thioredoxin and exhibits no glutaredoxin activity. We have also identified a group of previously unknown proteins from several other archaebacteria that have significant (34-44%) sequence identity with MtH895. These proteins have unusual active site -CXXC- motifs not found in any known thioredoxin or glutaredoxin. On the basis of the results presented here, we predict that these small proteins are all members of a new class of truncated thioredoxins.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Sudeepa
authors.initials: S
authors.lastname: Bhattacharyya
authors.forename: Bahram
authors.initials: B
authors.lastname: Habibi-Nazhad
authors.forename: Godwin
authors.initials: G
authors.lastname: Amegbey
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Slupsky
authors.forename: Adelinda
authors.initials: A
authors.lastname: Yee
authors.forename: Cheryl
authors.initials: C
authors.lastname: Arrowsmith
authors.forename: David S
authors.initials: DS
authors.lastname: Wishart
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D017014:Methanobacterium / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D012996:Solutions; D013816:Thermodynamics; D013879:Thioredoxins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D012996:Solutions; D013879:Thioredoxins; C034970:bacteriophage T7 induced DNA polymerase; D004259:DNA-Directed DNA Polymerase