title: The crystal structure of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase reveals distinct domain homologies.
abstract: BACKGROUND
  Glucose homeostasis is maintained by the processes of glycolysis and gluconeogenesis. The importance of these pathways is demonstrated by the severe and life threatening effects observed in various forms of diabetes. The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase catalyzes both the synthesis and degradation of fructose-2,6-bisphosphate, a potent regulator of glycolysis. Thus this bifunctional enzyme plays an indirect yet key role in the regulation of glucose metabolism.
  
  
  RESULTS
  We have determined the 2.0 A crystal structure of the rat testis isozyme of this bifunctional enzyme. The enzyme is a homodimer of 55 kDa subunits arranged in a head-to-head fashion, with each monomer consisting of independent kinase and phosphatase domains. The location of ATPgammaS and inorganic phosphate in the kinase and phosphatase domains, respectively, allow us to locate and describe the active sites of both domains.
  
  
  CONCLUSIONS
  The kinase domain is clearly related to the superfamily of mononucleotide binding proteins, with a particularly close relationship to the adenylate kinases and the nucleotide-binding portion of the G proteins. This is in disagreement with the broad speculation that this domain would resemble phosphofructokinase. The phosphatase domain is structurally related to a family of proteins which includes the cofactor independent phosphoglycerate mutases and acid phosphatases.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235-8884, USA. hasemann@howie.swmed.edu
authors.forename: C A
authors.initials: CA
authors.lastname: Hasemann
authors.forename: E S
authors.initials: ES
authors.lastname: Istvan
authors.forename: K
authors.initials: K
authors.lastname: Uyeda
authors.forename: J
authors.initials: J
authors.lastname: Deisenhofer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D019204:GTP-Binding Proteins / Q000737:chemistry; D008297:Male; D008969:Molecular Sequence Data; D025481:Phosphofructokinase-2; D010736:Phosphoglycerate Mutase / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry*; D011487:Protein Conformation; D051381:Rats; D013737:Testis / Q000201:enzymology
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); D025481:Phosphofructokinase-2; D010744:Phosphoric Monoester Hydrolases; D019204:GTP-Binding Proteins; D010736:Phosphoglycerate Mutase