title: Structural and functional characterisation of the methionine adenosyltransferase from Thermococcus kodakarensis.
abstract: BACKGROUND
  Methionine adenosyltransferases catalyse the synthesis of S-adenosylmethionine, a cofactor abundant in all domains of life. In contrast to the enzymes from bacteria and eukarya that show high sequence similarity, methionine adenosyltransferases from archaea diverge on the amino acid sequence level and only few conserved residues are retained.
  
  
  RESULTS
  We describe the initial characterisation and the crystal structure of the methionine adenosyltransferase from the hyperthermophilic archaeon Thermococcus kodakarensis. As described for other archaeal methionine adenosyltransferases the enzyme is a dimer in solution and shows high temperature stability. The overall structure is very similar to that of the bacterial and eukaryotic enzymes described, with some additional features that might add to the stability of the enzyme. Compared to bacterial and eukaryotic structures, the active site architecture is largely conserved, with some variation in the substrate/product-binding residues. A flexible loop that was not fully ordered in previous structures without ligands in the active side is clearly visible and forms a helix that leaves an entrance to the active site open.
  
  
  CONCLUSIONS
  The similar three-dimensional structures of archaeal and bacterial or eukaryotic methionine adenosyltransferases support that these enzymes share an early common ancestor from which they evolved independently, explaining the low similarity in their amino acid sequences. Furthermore, methionine adenosyltransferase from T. kodakarensis is the first structure without any ligands bound in the active site where the flexible loop covering the entrance to the active site is fully ordered, supporting a mechanism postulated earlier for the methionine adenosyltransferase from E. coli. The structure will serve as a starting point for further mechanistic studies and permit the generation of enzyme variants with different characteristics by rational design.
authors.forename: Julia
authors.initials: J
authors.lastname: Schlesier
authors.forename: Jutta
authors.initials: J
authors.lastname: Siegrist
authors.forename: Stefan
authors.initials: S
authors.lastname: Gerhardt
authors.forename: Annette
authors.initials: A
authors.lastname: Erb
authors.forename: Simone
authors.initials: S
authors.lastname: Blaesi
authors.forename: Michael
authors.initials: M
authors.lastname: Richter
authors.forename: Oliver
authors.initials: O
authors.lastname: Einsle
authors.affiliation: Institute of Pharmaceutical Sciences, Albert-Ludwigs-University Freiburg, Albertstr, 25, Freiburg D-79104, Germany. jennifer.andexer@pharmazie.uni-freiburg.de.
authors.forename: Jennifer N
authors.initials: JN
authors.lastname: Andexer
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D002942:Circular Dichroism; D003001:Cloning, Molecular; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D008716:Methionine Adenosyltransferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D012436:S-Adenosylmethionine / Q000378:metabolism*; D016415:Sequence Alignment; D019712:Thermococcus / Q000201:enzymology* / Q000235:genetics
chemical_list: D012436:S-Adenosylmethionine; D008716:Methionine Adenosyltransferase