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Phosphatidylinositol consists of a family of lipids as illustrated on the right, a class of the phosphatidylglycerides. In such molecules the isomer of the inositol group is assumed to be the myo- conformer unless otherwise stated. Typically phosphatidylinositols form a minor component on the cytosolic side of eukaryotic cell membranes. The phosphate group gives the molecules a negative charge at physiological pH.

The form of phosphatidylinositol comprising the isomer muco-inositol acts as a sensory receptor in the taste function of the sensory system. In this context it is often referred to as PtdIns, but that does not imply any molecular difference from phosphatidylinositols comprising the myo- conformers of inositol.

The phosphatidylinositol can be phosphorylated to form phosphatidylinositol phosphate (PI-4-P, referred to as PIP in close context or informally), phosphatidylinositol bisphosphate (PIP₂) and phosphatidylinositol trisphosphate (PIP₃). All lipids based on phosphatidylinositol are known as inositides, or sometimes phosphoinositides.

Biosynthesis

The neurologically important PtdIns are synthesized as a liquid crystalline region in the outer lemma of the cilia of the sodium path (Na path) sensory receptors exposed to the mucosa in mammals and some other vertebrates (Family Chordata). This specific form of phosphatidylinositol formed with muco-Inositol (CAS 488-55-1) is NOT shown at right. This compound forms the sensory receptor of the sodium path under the molecular biochemical model of the gustatory modality.

Biosynthesis of phosphatidylinositol catalyzed by phosphatidylinositol synthase. Figure adapted from Christopher, K.; van Holde, K.E.; Ahern, Kevin G. Biochemistry Third Edition. Pearson Education, Inc: Singapore, 2005; p 678.^[1]

The synthesis of phosphatidylinositol in the laboratory is catalyzed by phosphatidylinositol synthase and involves CDP-diacylglycerol and L-myo-inositol.^[1]

Chemistry

PI has a polar and non-polar region, making the lipid an amphiphile. Phosphatidylinositol is classified as a glycerophospholipid that contains a glycerol backbone, two non-polar fatty acid tails, a phosphate group substituted with an inositol polar head group.

The most common fatty acids of phosphoinositides are stearic acid in the SN₁ position and arachidonic acid, in the SN₂ position. Hydrolysis of phosphoinositides yield one mole of glycerol, two moles of fatty acids, one mole of inositol and one, two, or three moles of phosphoric acids, depending on the number of phosphates on the inositol rings. Phosphoinositides are regarded as the most acidic phospholipids.

The specific fatty acids of PdtIns, and their conformation, employed in the sensory neurons has not been elucidated.

Phosphoinositides

Phosphorylated forms of phosphatidylinositol (PI) are called phosphoinositides and play important roles in lipid signaling, cell signaling and membrane trafficking. The inositol ring can be phosphorylated by a variety of kinases on the three, four and five hydroxyl groups in seven different combinations. However, the two and six hydroxyl group is typically not phosphorylated due to steric hindrance.

All seven variations of the following phosphoinositides have been found in animals:

Phosphatidylinositol monophosphates:

Phosphatidylinositol 3-phosphate, also known as PtdIns3P or PI(3)P
Phosphatidylinositol 4-phosphate, also known as PtdIns4P or PI(4)P
Phosphatidylinositol 5-phosphate, also known as PtdIns5P or PI(5)P

Phosphatidylinositol bisphophosphates:

Phosphatidylinositol 3,4-bisphosphate, also known as PtdIns(3,4)P or PI(3,4)P₂
Phosphatidylinositol 3,5-bisphosphate, also known as PtdIns(3,5)P or PI(3,5)P₂
Phosphatidylinositol 4,5-bisphosphate, also known as PtdIns(4,5)P, PI(4,5)P₂ or often simply referred to as PIP₂

Phosphatidylinositol trisphophosphate:

Phosphatidylinositol 3,4,5-trisphosphate, also known as PtdIns(3,4,5)P or PI(3,4,5)P₃

These phosphoinositides are also found in plant cells, with the exception of PIP₃.^[2]

References

^ ^a ^b Mathews, Chrisotphe K.; van Holde, K.E.; Ahern, Kevin G. (2005). Biochemistry Third Edition.
^ Muller-Roeber B, Pical C; , (2002). Inositol Phospholipid Metabolism in Arabidopsis. Characterized and Putative Isoforms of Inositol Phospholipid Kinase and Phosphoinositide-Specific Phospholipase C.

Additional images

Membrane lipids
Phosphatidyl-inositol
Inositol
Glycerol

External links

Phosphatidylinositols at the US National Library of Medicine Medical Subject Headings (MeSH)
Phosphatidylinositol at Lipid Library

UpToDate Contents

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1. T細胞受容体シグナル伝達 t cell receptor signaling

English Journal

Lipidomic profiling of dried seahorses by hydrophilic interaction chromatography coupled to mass spectrometry.

Shen Q1, Dai Z2, Huang YW3, Cheung HY4.
Food chemistry.Food Chem.2016 Aug 15;205:89-96. doi: 10.1016/j.foodchem.2016.02.151. Epub 2016 Mar 3.
Dried seahorse is a precious raw food material for cooking soups. In this study, a lipidomics strategy using the techniques of solid-phase extraction (SPE) and hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-QTOF/MS) was developed for extraction, visualization, and quantificat
PMID 27006218

Ice nucleation of an insect lipoprotein ice nucleator (LPIN) correlates with retardation of the hydrogen bond dynamics at the myo-inositol ring.

Bäumer A1, Duman JG2, Havenith M1.
Physical chemistry chemical physics : PCCP.Phys Chem Chem Phys.2016 Jul 4. [Epub ahead of print]
Remarkably little is known about the mechanism of action of ice nucleation proteins (INPs), although their ability to trigger ice nucleation could be used in a broad variety of applications. We present CD measurements of an insect lipoprotein ice nucleator (LPIN) which show that the lipoproteins con
PMID 27373225

Alteration of phospholipids during the mitophagic process in lung cancer cells.

Lee JW1, Cho KM1, Jung JH1, Tran Q2, Jung W3, Park J2, Kim KP1.
Journal of microbiology and biotechnology.J Microbiol Biotechnol.2016 Jun 30. doi: 10.4014/jmb.1604.04031. [Epub ahead of print]
MALDI-TOF/MS was applied to investigate alterations in phospholipids in mitophagic cancer cells. Several phospholipids, including phosphatidylcholines (PC), sphingomyelins (SM), and phosphatidylinositols (PI), were successfully analyzed in control and mitophagy-induced H460 cells in the positive and
PMID 27363475

Japanese Journal

3K0912 cAMP刺激に対するPtdIns(3,4,5)P3応答の不均一性(細胞生物的課題3,第49回年会講演予稿集)

Nishikawa Masatoshi,Ueda Masahiro,Shibata Tatsuo
生物物理 51(SUPPLEMENT_1), S143-S144, 2011-08-15
NAID 110008903572

PIPKs are essential for rhizoid elongation and caulonemal cell development in the moss Physcomitrella patens

Saavedra Laura,Balbi Virginia,Lerche Jennifer,Mikami Koji,Heilmann Ingo,Sommarin Marianne
The plant journal 67(4), 635-647, 2011-08-00
… PtdIns-4,5-bisphosphate is a lipid messenger of eukaryotic cells playing critical roles inprocesses such as cytoskeleton organization, intracellular vesicular trafficking, secretion,cell motility, regulation of ion channels and nuclear signalling pathways. … The enzymesresponsible for the synthesis of PtdIns(4,5)P2 are phosphatidylinositol phosphate kinases(PIPKs). …
NAID 120004608957

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★リンクテーブル★

リンク元	「phosphoinositide」「PI」「ホスファチジルイノシトール」「inositol phospholipid」
拡張検索	「PtdIns 3-kinase」「PtdIns 4-kinase」「PtdIns-4,5-P2」

「phosphoinositide」

Phosphatidylinositol
Names
	Other names PI, PtdIns
Properties
Chemical formula	C47H83O13P
Molar mass	886.56 g/mol, neutral with fatty acid composition - 18:0, 20:4
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references