Question

Explain the overall structure of phosphofructokinase 2/ fructose diphosphate 2, noting why the protein interface is important, and the role of serine 32.

Answer 1

Phosphofructokinase 2

Phosphofructokinase 2 (6-phosphofructo-2-kinase, PFK2) or fructose bisphosphatase 2 (FBPase2), is an enzyme responsible for regulating the rates of glycolysis and gluconeogenesis in the human body. Specifically, it regulates formation and degradation of metabolite fructose-2,6-bisphosphatase (Fru-2,6-P2) which activates enzyme PFK1 in the glycolysis pathway.The structure of PFK2 enables it to act as a bifunctional enzyme. It is a homodimer of 55 kDa subunits arranged in a head-to-head fashion, with each polypeptide chain consisting of independent kinase and phosphatase domain. When Ser-32 of the bifunctional protein is phosphorylated, the negative charge causes the conformation change of the enzyme to favor the FBPase2 activity; otherwise, PFK2 activity is favored.The PFK2 domain is closely related to the superfamily of mononucleotide binding proteins including adenylate cyclase, whereas that of FBPase2 is related to a family of histidine phosphatase and proteins that include phosphoglycerate mutases.The monomers of the bifunctional protein are clearly divided into two functional domains. The kinase domain is located on the N-terminal.It consists of a central six-stranded β sheet, with five parallel strands and an antiparallel edge strand, surrounded by seven α helices. The domain contains nucleotide-binding fold at the C-terminal end of the first β-strand and thus resembles the structure of adenylate kinase.

On the other hand, the phosphatase domain is located on the C-terminal.It resembles the family of proteins that include phosphoglycerate mutases (PGMs) and acid phosphatases.The domain has a mixed α/ β structure, with a six-stranded central β sheet, plus an additional α-helical subdomain that covers the presumed active site of the molecule Finally, N-terminal region modulates PFK2 and FBPase2 activities, and stabilizes the dimer form of the enzyme.

Fructose diphosphate 2

Fructose 2,6-bisphosphate, abbreviated Fru-2,6-P2, is a metabolite that allosterically affects the activity of the enzymes phosphofructokinase 1 and fructose 1,6-bisphosphatase to regulate glycolysis and gluconeogenesis. Fru-2,6-P2 is synthesized and broken down by the bifunctional enzyme phosphofructokinase 2/fructose-2,6-bisphosphatase .The synthesis of Fru-2,6-P2 is performed through a bifunctional enzyme containing both PFK-2 and FBPase-2, which is dephosphorylated, allowing the PFK-2 portion to phosphorylate fructose 6-phosphate using ATP. The breakdown of Fru-2,6-P2 is catalyzed by the phosphorylation of the bifunctional enzyme, which allows FBPase-2 to dephosphorylate fructose 2,6-bisphosphate to produce fructose 6-phosphate and Pi

Note:Role of serine is included in phosphofructokinase 2 structure