title: The crystal structure of an engineered monomeric triosephosphate isomerase, monoTIM: the correct modelling of an eight-residue loop.
abstract: BACKGROUND
  The triosephosphate isomerase (TIM) fold is found in several different classes of enzymes, most of which are oligomers; TIM itself always functions as a very tight dimer. It has recently been shown that a monomeric form of TIM ('monoTIM') can be constructed by replacing a 15-residue interface loop, loop-3, with an eight-residue fragment; modelling suggests that this should result in a short strain-free turn, resulting in the subsequent helix, helix-A3, having an additional turn at its amino terminus.
  
  
  RESULTS
  The crystal structure of monoTIM shows that it retains the characteristic TIM-barrel (betaalpha)8-fold and that the new loop has a structure very close to that predicted. Two other interface loops, loop-1 and loop-4, which contain the active site residues Lys13 and His95, respectively, show significant changes in structure in monoTIM compared with dimeric wild-type TIM.
  
  
  CONCLUSIONS
  The observed structural differences between monoTIM and wild-type TIM indicate that the dimeric appearance of TIM determines the location and conformation of two of the four catalytic residues.
authors.affiliation: European Molecular Biology Laboratory, Meyerhofstrasse 1, Postfach 102209, D69012 Heidelberg, Germany.
authors.forename: T V
authors.initials: TV
authors.lastname: Borchert
authors.forename: R
authors.initials: R
authors.lastname: Abagyan
authors.forename: K V
authors.initials: KV
authors.lastname: Kishan
authors.forename: J P
authors.initials: JP
authors.lastname: Zeelen
authors.forename: R K
authors.initials: RK
authors.lastname: Wierenga
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D006639:Histidine / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D015202:Protein Engineering; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014305:Triose-Phosphate Isomerase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D006639:Histidine; D014305:Triose-Phosphate Isomerase; D008239:Lysine