6-Phosphofructo-2-Kinase/Fructose-2,6-Bisphosphatase: A Metabolic Signaling Enzyme

Molecular cloning and tissue‐specific expression of mouse kidney 6‐phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatase

“…Amino acids which are identical between all four isozymes are enclosed in boxes. Shaded boxes contain conserved catalytic and substrate binding sites [12]. Using numbering based on rat liver sequence, these sites include: Arg452, Lys-356, and Arg-360, residues shown to bind substrate and/or product which are found on a surface loop of all mammalian FBPases; His-258, Glu-327 and His-392, a trio of catalytic residues in rat liver [30,12]; Arg-195, a key residue involved in Fru-6-P binding [31]; Arg-257 and Arg-307, which associate with the reactive C-2 phospho group of Fru-2,6-P2 [30,32]; and the ATP binding site, GlyLeu-Pro-Ala-Arg-Gly-Lys-Thr [33].…”

“…3). PFK-2/FBPase-2 catalytic and substrate binding site residues have been identified in rat liver [12] and the majority of these sites were found to be conserved throughout the mammalian isoforms, including the newly isolated mouse heart-type clone. Comparison of the predicted amino acid sequence of mouse heart-type clone to previously characterized PFK-2/FBPase-2 isozymes in other species reveals interesting homologies with respect to evolution of the enzyme.…”

“…In rat, gene A is a 60 kb X-linked locus encoding the liver, muscle and fetal isozyme transcripts [9,10], while gene B is a 22 kb autosomal locus encoding the heart isozyme [11]. PFK-2/FBPase-2 is one of only five known bifunctional enzymes which catalyze opposing reactions and is unique because it is the only one whose target is a metabolite rather than a protein [12].…”

Interdomain Communications in Bifunctional Enzymes: How Are Different Activities Coordinated?

“…The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6-PF-2K/Fru-2,6-BPase) plays a major role in the control of hepatic gluconeogenetic/glycolytic fluxes as the sole enzyme responsible for both the synthesis and degradation of fructose -2,6-bisphosphate (Fru-2,6-P 2 ) and thereby modulating the intracellular concentration of this signal metabolite (6,30). The three-dimensional structure of the rat liver enzyme (31) reveals two independent catalytic domains per each 55 kDa monomer of the dimeric molecule: the N-terminal kinase domain and the C-terminal phosphatase domain, which catalyze the opposing reactions.…”

“…The bisphosphatase reaction proceeds via a covalent phosphohistidine intermediate formed upon reaction with Fru-2,6-P 2 (6,30). These activities are regulated reciprocally by cAMP-dependent protein kinase (PKA)-mediated phosphorylation, which takes place at a single serine residue in the N-terminal tail of the molecule (32).…”