Phytase

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A phytase (myo-inositol hexakisphosphate phosphohydrolase) is any type of phosphatase enzyme that catalyzes the hydrolysis of phytic acid (myo-inositol hexakisphosphate) – an indigestible, organic form of phosphorus that is found in grains and oil seeds – and releases a usable form of inorganic phosphorus.[1] While phytases have been found to occur in animals, plants, fungi and bacteria, phytases have been most commonly detected and characterized from fungi.[2]

Classes[edit]

Four distinct classes of phytase have been characterized in the literature: histidine acid phosphatases (HAPS), B-propeller phytases, purple acid phosphatases,[2] and most recently, protein tyrosine phosphatase-like phytases (PTP-like phytases).[3]

Histidine acid phosphatases (HAPs)[edit]

Most of the known phytases belong to a class of enzyme called histidine acid phosphatases (HAPs). HAPs have been isolated from filamentous fungi, bacteria, yeast, and plants.[1] All members of this class of phytase share a common active site sequence motif (Arg-His-Gly-X-Arg-X-Pro) and have a two-step mechanism that hydrolyzes phytic acid (as well as some other phosphoesters).[2] The phytase from the fungus Aspergillus niger is a HAP and is well known for its high specific activity and its commercially marketed role as an animal feed additive to increase the bioavailability of phosphate from phytic acid in the grain-based diets of poultry and swine.[4] HAPs have also been overexpressed in several transgenic plants as a potential alternative method of phytase production for the animal feed industry[5] and very recently, the HAP phytase gene from E. coli has been successfully expressed in a transgenic pig.[6]

β-propeller phytases[edit]

β-propeller phytases make up a recently discovered class of phytase. These first examples of this class of enzyme were originally cloned from Bacillus species,[2] but numerous microorganisms have since been identified as producing β-propeller phytases.[7] The three-dimensional structure of β-propeller phytase is similar to a propeller with six blades. Current research suggests that β-propeller phytases are the major phytate-degrading enzymes in water and soil, and may play a major role in phytate-phosphorus cycling.[7]

Purple acid phosphatases[edit]

A phytase has recently been isolated from the cotyledons of germinating soybeans that has the active site motif of a purple acid phosphatase (PAP). This class of metalloenzyme has been well studied and searches of genomic databases reveal PAP-like sequences in plants, mammals, fungi, and bacteria. However, only the PAP from soybeans has been found to have any significant phytase activity. The three-dimensional structure, active-site sequence motif and proposed mechanism of catalysis have been determined for PAPs.[citation needed]

Protein tyrosine phosphatase-like phytases[edit]

Only a few of the known phytases belong to a superfamily of enzymes called protein tyrosine phosphatases (PTPs). PTP-like phytases, a relatively newly discovered class of phytase, have been isolated from bacteria that normally inhabit the gut of ruminant animals.[8] All characterized PTP-like phytases share an active site sequence motif (His-Cys-(X)5-Arg), a two-step, acid-base mechanism of dephosphorylation, and activity towards phosphrylated tyrosine residues, characteristics that are common to all PTP superfamily enzymes.[9][10] Like many PTP superfamily enzymes, the exact biological substrates and roles of bacterial PTP-like phytases have not yet been clearly identified.[3] Interestingly, the characterized PTP-like phytases from ruminal bacteria share sequence and structural homology with the mammalian PTP-like phosphoinositide/-inositol phosphatase PTEN,[3] and significant sequence homology to the PTP domain of a type III-secreted virulence protein from Pseudomonas syringae (HopPtoD2).[11]

Biochemical characteristics[edit]

Substrate specificity[edit]

Most phytases show a broad substrate specificity, having the ability to hydrolyze many phosphorylated compounds that are not structurally similar to phytic acid such as ADP, ATP, phenyl phosphate, fructose 1,6-bisphosphate, glucose 6-phosphate, glycerophosphate and 3-phosphoglycerate.[12] Only a few phytases have been described as highly specific for phytic acid, such as phytases from Bacillus sp., Aspergillus sp., E. coli[12] and those phytases belonging to the class of PTP-like phytases[9]

Pathways of phytic acid dephosphorylation[edit]

Phytic acid has six phosphate groups that may be released by phytases at different rates and in different order. Phytases hydrolyze phosphates from phytic acid in a stepwise manner, yielding products that again become substrates for further hydrolysis. Most phytases are able to cleave five of the six phosphate groups from phytic acid.[12] Phytases have been grouped based on the first phosphate position of phytic acid that is hydrolyzed. The Enzyme Nomenclature Committee of the International Union of Biochemistry recognizes three types of phytases based on the position of the first phosphate hydrolyzed, those are 3-phytase (EC 3.1.3.8), 4-phytase (EC 3.1.3.26), and 5-phytase (EC 3.1.3.72). To date, most of the known phytases are 3-phytases or 4-phytases,[12] only a HAP purified from lily pollen[13] and a PTP-like phytase from Selenomonas ruminantium subsp. lactilytica[11] have been determined to be 5-phytases.

Biological relevance[edit]

Phytic acid and its metabolites have several important roles in seeds and grains, most notably, phytic acid functions as a phosphorus store, as an energy store, as a source of cations and as a source of myo-inositol (a cell wall precursor).[14] Phytic acid is the principal storage forms of phosphorus in plant seeds and the major source of phosphorus in the grain-based diets used in intensive livestock operations. The organic phosphate found in phytic acid is largely unavailable to the animals that consume it, but the inorganic phosphate that phytases release can be easily absorbed. Ruminant animals can use phytic acid as a source of phosphorus because the bacteria that inhabit their gut are well characterized producers of many types of phytases. However, monogastric animals do not carry bacteria that produce phytase, thus, these animals cannot use phytic acid as a major source of phosphorus and it is excreted in the feces.[14]

Phytic acid and its metabolites have several other important roles in Eukaryotic physiological processes. As such, phytases, which hydrolyze phytic acid and its metabolites, also have important roles. Phytic acid and its metabolites have been implicated in DNA repair, clathrin-coated vesicular recycling, control of neurotransmission and cell proliferation.[15][16][17] The exact roles of phytases in the regulation of phytic acid and its metabolites and the resulting role in the physiological processes described above are still largely unknown and the subject of much research.

Phytase has been reported to cause hypersensitivity pneumonitis in a human exposed while adding the enzyme to cattle feed.[18][19]

Agricultural and industrial uses[edit]

Phytase is produced by bacteria found in the gut of ruminant animals (cattle, sheep) making it possible for them to use the phytic acid found in grains as a source of phosphorus.[20] Non-ruminants (monogastric animals) like human beings, dogs, birds, etc. do not produce phytase. Research in the field of animal nutrition has put forth the idea of supplementing feed with phytase so as to make available to the animal phytate-bound nutrients like calcium, phosphorus, other minerals, carbohydrates and proteins.

Phytase is used as an animal feed supplement – often in poultry and swine – to enhance the nutritive value of plant material by liberation of inorganic phosphate from phytic acid (myo-inositol hexakisphosphate). Phytase can be purified from transgenic microbes and has been produced recently in transgenic canola, alfalfa and rice plants. Phytase can also be produced on a large scale through cellulosic biomass fermentation using genetically modified (GM) yeast. Phytase can also be isolated from basidiomycetes fungi. The Enviropig, a strain of transgenic pig, can produce phytase, reducing its environmental impact.[21]

References[edit]

  1. ^ a b Mullaney EJ, Daly CB, Ullah AH (2000). "Advances in phytase research". Adv Appl Microbiol 47: 157–199. doi:10.1016/S0065-2164(00)47004-8. PMID 12876797. 
  2. ^ a b c d Mullaney EJ, Ullah AH (2003). "The term phytase comprises several different classes of enzymes". Biochem Biophys Res Commun 312 (1): 179–184. doi:10.1016/j.bbrc.2003.09.176. PMID 14630039. 
  3. ^ a b c Puhl AA, Gruninger RJ, Greiner R, Janzen TW, Mosimann SC, Selinger LB (2007). "Kinetic and structural analysis of a bacterial protein tyrosine phosphatase-like myo-inositol polyphosphatase". Protein Science 16 (7): 1368–1378. doi:10.1110/ps.062738307. PMC 2206706. PMID 17567745. 
  4. ^ Kim T, Mullaney EJ, Porres JM, Roneker KR, Crowe S, Rice S, Ko T, Ullah AH, Daly CB, Welch R, Lei XG (2006). "Shifting the pH profile of Aspergillus niger PhyA phytase to match the stomach pH enhances its effectiveness as an animal feed additive". Appl Environ Microbiol 72 (6): 4397–4403. doi:10.1128/AEM.02612-05. PMC 1489644. PMID 16751556. 
  5. ^ Chen R, Xue G, Chen P, Yao B, Yang W, Ma Q, Fan Y, Zhao Z, Tarczynski MC, Shi J (2006). "Transgenic maize plants expressing a fungal phytase gene". Transgenic Res 17 (4): 633–643. doi:10.1007/s11248-007-9138-3. PMID 17932782. 
  6. ^ Golovan SP, Meidinger RG, Ajakaiye A, Cottrill M, Wiederkehr MZ, Barney DJ, Plante C, Pollard JW, Fan MZ, Hayes MA, Laursen J, Hjorth JP, Hacker RR, Phillips JP, Forsberg CW (2006). "Pigs expressing salivary phytase produce low-phosphorus manure". Nat Biotechnol 19 (8): 741–745. doi:10.1038/90788. PMID 11479566. 
  7. ^ a b Lim BL, Yeung P, Cheng C, Hill JE (2007). "Distribution and diversity of phytate-mineralizing bacteria". Isme J. 1 (4): 321–330. doi:10.1038/ismej.2007.40. PMID 18043643. 
  8. ^ Nakashima BA, McAllister TA, Sharma R, Selinger LB (2007). "Diversity of phytases in the rumen". Microb Ecol 53 (1): 82–88. doi:10.1007/s00248-006-9147-4. PMID 17186149. 
  9. ^ a b Puhl AA, Greiner R, Selinger LB (2009). "Stereospecificity of myo-inositol hexakisphosphate hydrolysis by a protein tyrosine phosphatase-like inositol polyphosphatase from Megasphaera elsdenii". Appl Microbiol Biotechnol 82 (1): 95–103. doi:10.1007/s00253-008-1734-5. PMID 18853154. 
  10. ^ Zhang ZY (2003). "Mechanistic studies on protein tyrosine phosphatases". Prog. Nucleic Acid Res. Mol. Biol 73: 171–220. doi:10.1016/S0079-6603(03)01006-7. PMID 12882518. 
  11. ^ a b Puhl A, Greiner R, Selinger LB (2008). "A protein tyrosine phosphatase-like inositol polyphosphatase from Selenomonas ruminantium subsp. lactilytica has specificity for the 5-phosphate of myo-inositol hexakisphosphate". The International Journal of Biochemistry & Cell Biology 40 (10): 2053–2064. doi:10.1016/j.biocel.2008.02.003. PMID 18358762. 
  12. ^ a b c d Konietzny U, Greiner R (2002). "Molecular and catalytic properties of phytate-degrading enzymes (phytases)". Int J Food Sci Technol 37: 791–812. doi:10.1046/j.1365-2621.2002.00617.x. 
  13. ^ Barrientos L, Scott JJ, Murthy, PPN (1994). "Specificity of hydrolysis of phytic acid by alkaline phytase from lily pollen". Plant Physiology 106 (4): 1489–1495. doi:10.1104/pp.106.4.1489. PMC 159689. PMID 7846160. 
  14. ^ a b Reddy NR, Sathe SK, Salunkhe DK (1982). "Phytates in legumes and cereals". Adv Food Res 28: 1–92. doi:10.1016/s0065-2628(08)60110-x. PMID 6299067. 
  15. ^ Conway SJ, Miller GJ (2007). "Biology-enabling inositol phosphates, phosphatidylinositol phosphates and derivatives". Nat Prod Rep 24 (4): 687–707. doi:10.1039/b407701f. PMID 17653355. 
  16. ^ Brailoiu E, Miyamoto MD, Dun NJ (2003). "Inositol derivatives modulate spontaneous transmitter release at the frog neuromuscular junction.". Neuropharmacology 45 (5): 691–701. doi:10.1016/S0028-3908(03)00228-4. PMID 12941382. 
  17. ^ Bunce MW, Bergendahl K, Anderson RA (2006). "Nuclear PI(4,5)P(2): a new place for an old signal". Biochim Biophys Acta 1761 (5–6): 560–569. doi:10.1016/j.bbalip.2006.03.002. PMID 16750654. 
  18. ^ Girard M, Cormier Y (2010). "Hypersensitivity pneuomonitis". Current Opinion in Allergy and Clinical Immunology 10 (2): 99–103. doi:10.1097/ACI.0b013e3283373bb8. PMID 20093932. 
  19. ^ van Heemst RC, Sander I, Rooyackers J, et al (2009). "Hypersensitivity pneumonitis caused by occupational exposure to phytase". Eur Respir J 33 (6): 1507–09. doi:10.1183/09031936.00035408. PMID 19483053. 
  20. ^ Frias, J.; Doblado, R.; Antezana, J. R.; Vidal-Valverde, C. N. (2003). "Inositol phosphate degradation by the action of phytase enzyme in legume seeds". Food Chemistry 81 (2): 233. doi:10.1016/S0308-8146(02)00417-X.  edit
  21. ^ Golovan, S. P., Meidinger, R. G., Ajakaiye, A., Cottrill, M., Wiederkehr, M. Z., Barney, D. J., ... & Forsberg, C. W. (2001). Pigs expressing salivary phytase produce low-phosphorus manure. Nature biotechnology, 19(8), 741–745. Retrieved from http://www.nature.com/nbt/journal/v19/n8/abs/nbt0801_741.html

See also[edit]