title: Crystal structure of transaldolase B from Escherichia coli suggests a circular permutation of the alpha/beta barrel within the class I aldolase family.
abstract: BACKGROUND
  Transaldolase is one of the enzymes in the non-oxidative branch of the pentose phosphate pathway. It transfers a C3 ketol fragment from a ketose donor to an aldose acceptor. Transaldolase, together with transketolase, creates a reversible link between the pentose phosphate pathway and glycolysis. The enzyme is of considerable interest as a catalyst in stereospecific organic synthesis and the aim of this work was to reveal the molecular architecture of transaldolase and provide insights into the structural basis of the enzymatic mechanism.
  
  
  RESULTS
  The three-dimensional (3D) structure of recombinant transaldolase B from E. coli was determined at 1.87 A resolution. The enzyme subunit consists of a single eight-stranded alpha/beta-barrel domain. Two subunits form a dimer related by a twofold symmetry axis. The active-site residue Lys132 which forms a Schiff base with the substrate is located at the bottom of the active-site cleft.
  
  
  CONCLUSIONS
  The 3D structure of transaldolase is similar to structures of other enzymes in the class I aldolase family. Comparison of these structures suggests that a circular permutation of the protein sequence might have occurred in transaldolase, which nevertheless results in a similar 3D structure. This observation provides evidence for a naturally occurring circular permutation in an alpha/beta-barrel protein. It appears that such genetic permutations occur more frequently during evolution than was previously thought.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Jia
authors.forename: W
authors.initials: W
authors.lastname: Huang
authors.forename: U
authors.initials: U
authors.lastname: Schörken
authors.forename: H
authors.initials: H
authors.lastname: Sahm
authors.forename: G A
authors.initials: GA
authors.lastname: Sprenger
authors.forename: Y
authors.initials: Y
authors.lastname: Lindqvist
authors.forename: G
authors.initials: G
authors.lastname: Schneider
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D019143:Evolution, Molecular; D005634:Fructose-Bisphosphate Aldolase / Q000737:chemistry / Q000145:classification / Q000235:genetics; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010427:Pentose Phosphate Pathway / Q000235:genetics; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012545:Schiff Bases / Q000737:chemistry; D016415:Sequence Alignment; D014153:Transaldolase / Q000737:chemistry*
chemical_list: D012545:Schiff Bases; D014153:Transaldolase; D005634:Fructose-Bisphosphate Aldolase