Inositol phosphatesare a group of mono- to hexaphosphorylatedinositols.Each form of inositol phosphate is distinguished by the number and position of the phosphate group on the inositol ring.
- inositol monophosphate (IP)
- inositol bisphosphate (IP2)
- inositol trisphosphate(IP3)
- inositol tetrakisphosphate (IP4)
- inositol pentakisphosphate(IP5)
- inositol hexaphosphate (IP6) also known asphytic acid,or phytate (as a salt).
A series of phosphorylation and dephosphorylation reactions are carried out by at least 19 phosphoinositidekinasesand 28 phosphoinositidephosphataseenzymes[1]allowing for the inter-conversion between the inositol phosphate compounds based on cellular demand.
Inositol phosphates play a crucial role in various signal transduction pathways responsible for cell growth and differentiation, apoptosis, DNA repair, RNA export, regeneration of ATP and more.
Functions
editInositol trisphosphate
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The inositol-phospholipid signaling pathway is responsible for the generation of IP3 through the cleavage ofPhosphatidylinositol 4,5-bisphosphate(PIP2) found in the lipid bi-layer of the plasma membrane byphospholipase Cin response to eitherreceptor tyrosine kinaseorGq alpha subunit-G protein-coupled receptorsignaling. Solubleinositol trisphosphate(IP3) is able to rapidly diffuse into the cytosol and bind to theinositol trisphosphate receptor(InsP3Rs) calcium channels located in the endoplasmic reticulum. This releases calcium into the cytosol, serving as a rapid and potent signal for various cellular processes.[1]
Further reading:Function of calcium in humans
Other
editInositol tetra-,penta-,and hexa-phosphates have been implicated ingene expression.[2][3]
Inositol hexaphosphate
editInositol hexaphosphate (IP6) is the most abundant inositol phosphate isomer found. IP6 is solely involved in various biological activities such as neurotransmission, immune response, regulation of kinase and phosphatase proteins as well as activation of calcium channels.[1]IP6 is also involved in ATP regeneration seen in plants as well as insulinexocytosisinpancreatic β cells.
Inositol hexaphosphate also facilitates the formation of the six-helix bundle and assembly of the immature HIV-1 Gag lattice. IP6 makes ionic contacts with two rings of lysine residues at the centre of the Gag hexamer. Proteolytic cleavage then unmasks an alternative binding site, where IP6 interaction promotes the assembly of the mature capsid lattice. These studies identify IP6 as a naturally occurring small molecule that promotes both assembly and maturation of HIV-1.[4]
References
edit- ^abcShamsuddin AK, Yang GY (2015-03-04). "Safety of Inositol and Inositol Phosphates". In Shamsuddin A, Yang GY (eds.).Inositol & its Phosphates: Basic Science to Practical Applications.Bentham Science Publishers. pp. 275–282.doi:10.2174/9781681080079115010024.ISBN9781681080079.
- ^Shen X, Xiao H, Ranallo R, Wu WH, Wu C (January 2003)."Modulation of ATP-dependent chromatin-remodeling complexes by inositol polyphosphates".Science.299(5603): 112–114.doi:10.1126/science.1078068.PMID12434013.S2CID8381889.
- ^Steger DJ, Haswell ES, Miller AL, Wente SR, O'Shea EK (January 2003)."Regulation of chromatin remodeling by inositol polyphosphates".Science.299(5603): 114–116.doi:10.1126/science.1078062.PMC1458531.PMID12434012.
- ^Dick RA, Zadrozny KK, Xu C, Schur FK, Lyddon TD, Ricana CL, et al. (August 2018)."Inositol phosphates are assembly co-factors for HIV-1".Nature.560(7719): 509–512.Bibcode:2018Natur.560..509D.doi:10.1038/s41586-018-0396-4.PMC6242333.PMID30069050.