The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes. One enzyme that utilizes this reaction is phosphofructokinase (PFK), which catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6- bisphosphate, a key regulatory step in the glycolytic pathway. It is allosterically inhibited by ATP and allosterically activated by AMP, thus indicating the cell's energetic needs when it undergoes the glycolytic pathway. PFK exists as a homotetramer in bacteria and mammals (where each monomer possesses 2 similar domains) and as an octomer in yeast (where there are 4 alpha- (PFK1) and 4 beta-chains (PFK2), the latter, like the mammalian monomers, possessing 2 similar domains). This protein may use the morpheein model of allosteric regulation.
PFK is about 300 amino acids in length, and structural studies of the bacterial enzyme have shown it comprises two similar (alpha/beta) lobes: one involved in ATP binding and the other housing both the substrate-binding site and the allosteric site (a regulatory binding site distinct from the active site, but that affects enzyme activity). The identical tetramer subunits adopt 2 different conformations: in a 'closed' state, the bound magnesium ion bridges the phosphoryl groups of the enzyme products (ADP and fructose-1,6- bisphosphate); and in an 'open' state, the magnesium ion binds only the ADP, as the 2 products are now further apart. These conformations are thought to be successive stages of a reaction pathway that requires subunit closure to bring the 2 molecules sufficiently close to react.
PFK belongs to the phosphofructokinase B (PfkB) family of sugar kinases. Other members of this family (also known as the Ribokinase family) include ribokinase (RK) adenosine kinase (AK), inosine kinase, and 1-phosphofructokinase. The members of the PfkB/RK family are identified by the presence of three conserved sequence motifs. The structures of several PfK family of proteins have been determined from a number of organisms and the enzymatic activity of this family of protein shows a dependence on the presence of pentavalent ions. PFK is found in isoform versions in skeletal muscle (PFKM), in the liver (PFKL), and from platelets (PFKP), allowing for tissue-specific expression and function. It is still speculated that the isoforms may play a role in specific glycolytic rates in the tissue-specific environments they are in. It has been found in humans that some human tumor cell lines had increased glycolytic productivity and correlated with the increased amount of PFKL.
Deficiency in PFK leads to glycogenosis type VII (Tarui's disease), an autosomal recessive disorder characterised by severe nausea, vomiting, muscle cramps and myoglobinuria in response to bursts of intense or vigorous exercise. Sufferers are usually able to lead a reasonably ordinary life by learning to adjust activity levels.
The reverse reaction is catalyzed by the enzyme Fructose-1,6-bisphosphatase.
There are two different phosphofructokinase enzymes in humans:
|Type||Synonyms||EC number||Substrate||Product||Paralog genes|
|PFKL, PFKM, PFKP|
|Phosphofructokinase 2||6-phosphofructo-2-kinase||EC 188.8.131.52||
|PFKFB1, PFKFB2, PFKFB3, PFKFB4|
- Evans PR, Hellinga HW (1987). "Mutations in the active site of Escherichia coli phosphofructokinase". Nature. 327 (6121): 437–439. Bibcode:1987Natur.327..437H. doi:10.1038/327437a0. PMID 2953977.
- Wegener G, Krause U (2002). "Different modes of activating phosphofructokinase, a key regulatory enzyme of glycolysis, in working vertebrate muscle". Biochem. Soc. Trans. 30 (2): 264–270. doi:10.1042/bst0300264. PMID 12023862.
- Raben N, Exelbert R, Spiegel R, Sherman JB, Nakajima H, Plotz P, Heinisch J (1995). "Functional expression of human mutant phosphofructokinase in yeast: genetic defects in French Canadian and Swiss patients with phosphofructokinase deficiency". Am. J. Hum. Genet. 56 (1): 131–141. PMC 1801305. PMID 7825568.
- Garrett, Reginald; Grisham, Reginald (2012). Biochemistry. Cengage Learning. p. 585. ISBN 978-1133106296.
- T. Selwood; E. K. Jaffe. (2011). "Dynamic dissociating homo-oligomers and the control of protein function". Arch. Biochem. Biophys. 519 (2): 131–43. doi:10.1016/j.abb.2011.11.020. PMC 3298769. PMID 22182754.
- Shirakihara Y, Evans PR (1988). "Crystal structure of the complex of phosphofructokinase from Escherichia coli with its reaction products". J. Mol. Biol. 204 (4): 973–994. doi:10.1016/0022-2836(88)90056-3. PMID 2975709.
- Park J, Gupta RS: Adenosine kinase and ribokinase--the RK family of proteins. Cell Mol Life Sci 2008, 65: 2875-2896.
- Bork P, Sander C, Valencia A: Convergent evolution of similar enzymatic function on different protein folds: the hexokinase, ribokinase, and galactokinase families of sugar kinases. Protein Sci 1993, 2: 31-40.
- Spychala J, Datta NS, Takabayashi K, Datta M, Fox IH, Gribbin T, Mitchell BS: Cloning of human adenosine kinase cDNA: sequence similarity to microbial ribokinases and fructokinases. Proc Natl Acad Sci U S A 1996, 93: 1232-1237.
- Maj MC, Singh B, Gupta RS: Pentavalent ions dependency is a conserved property of adenosine kinase from diverse sources: identification of a novel motif implicated in phosphate and magnesium ion binding and substrate inhibition. Biochemistry 2002, 41: 4059-4069.
- Sigrell JA, Cameron AD, Jones TA, Mowbray SL: Structure of Escherichia coli ribokinase in complex with ribose and dinucleotide determined to 1.8 A resolution: insights into a new family of kinase structures. Structure 1998, 6: 183-193.
- Sola-Penna, Mauro; Da Silva, Daniel; Coelho, Wagner S.; Marinho-Carvalho, Monica M.; Zancan, Patricia (November 2010). "Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism". IUBMB Life. 62 (11): 791–796. doi:10.1002/iub.393. ISSN 1521-6543. PMID 21117169.
- Ausina, Priscila; Da Silva, Daniel; Majerowicz, David; Zancan, Patricia; Sola-Penna, Mauro (July 2018). "Insulin specifically regulates expression of liver and muscle phosphofructokinase isoforms". Biomedicine & Pharmacotherapy. 103: 228–233. doi:10.1016/j.biopha.2018.04.033. ISSN 0753-3322. PMID 29655163.