Editing Inositol trisphosphate (section)

==Properties ==

===Chemical formula and molecular weight===
IP<sub>3</sub> is an organic molecule with a [[molecular mass]] of 420.10 g/mol. Its [[empirical formula]] is C<sub>6</sub>H<sub>15</sub>O<sub>15</sub>P<sub>3</sub>. It is composed of an [[inositol]] ring with three [[phosphate]] groups bound at the 1, 4, and 5 carbon positions, and three [[hydroxyl]] groups bound at positions 2, 3, and 6.<ref>{{PubChem|439456}}</ref>

===Chemical properties ===
Phosphate groups can exist in three different forms depending on a solution's [[pH]]. Phosphorus atoms can bind three oxygen atoms with single bonds and a fourth oxygen atom using a double/dative bond. The pH of the solution, and thus the form of the phosphate group determines its ability to bind to other molecules. The binding of phosphate groups to the inositol ring is accomplished by phosphor-ester binding (see [[phosphoric acids and phosphates]]). This bond involves combining a [[hydroxyl]] group from the inositol ring and a free phosphate group through a [[dehydration reaction]]. Considering that the average physiological pH is approximately 7.4, the main form of the phosphate groups bound to the inositol ring [[in vivo]] is PO<sub>4</sub><sup>2−</sup>. This gives IP<sub>3</sub> a net negative charge, which is important in allowing it to dock to its receptor, through binding of the phosphate groups to positively charged residues on the receptor. IP<sub>3</sub> has three [[hydrogen bond]] donors in the form of its three hydroxyl groups. The hydroxyl group on the 6th carbon atom in the inositol ring is also involved in IP<sub>3</sub> docking.<ref>{{cite journal|doi=10.1016/j.bbamcr.2004.09.016|title=Structural insights into the regulatory mechanism of IP3 receptor|year=2004|last1=Bosanac|first1=Ivan|last2=Michikawa|first2=Takayuki|last3=Mikoshiba|first3=Katsuhiko|last4=Ikura|first4=Mitsuhiko|journal=Biochimica et Biophysica Acta (BBA) - Molecular Cell Research|volume=1742|issue=1–3|pages=89–102|pmid=15590059|doi-access=}}</ref>

===Binding to its receptor===
[[File:IP3 moleucle.png|thumb|IP<sub>3</sub> anion with oxygen atoms (red) and the hydrogen atoms involved in docking to InsP3R (dark blue) indicated]]
The docking of IP<sub>3</sub> to its receptor, which is called the [[inositol trisphosphate receptor]] (InsP3R), was first studied using deletion [[mutagenesis]] in the early 1990s.<ref>{{Cite journal|pmid=2174351|year=1990|last1=Mignery|first1=GA|last2=Südhof|first2=TC|title=The ligand binding site and transduction mechanism in the inositol-1,4,5-triphosphate receptor|volume=9|issue=12|pages=3893–8|pmc=552159|journal=The EMBO Journal|doi=10.1002/j.1460-2075.1990.tb07609.x}}</ref> Studies focused on the [[N-terminus]] side of the IP<sub>3</sub> receptor. In 1997 researchers localized the region of the IP<sub>3</sub> receptor involved with binding of IP<sub>3</sub> to between [[amino acid]] residues 226 and 578 in 1997. Considering that IP<sub>3</sub> is a negatively charged molecule, positively charged amino acids such as [[arginine]] and [[lysine]] were believed to be involved. Two arginine residues at position 265 and 511 and one lysine residue at position 508 were found to be key in IP<sub>3</sub> docking. Using a modified form of IP<sub>3</sub>, it was discovered that all three phosphate groups interact with the receptor, but not equally. Phosphates at the 4th and 5th positions interact more extensively than the phosphate at the 1st position and the hydroxyl group at the 6th position of the inositol ring.<ref>{{cite journal|doi=10.1016/j.tibs.2004.02.010|title=IP3 receptors: The search for structure|year=2004|last1=Taylor|first1=Colin W.|last2=Da Fonseca|first2=Paula C.A.|last3=Morris|first3=Edward P.|journal=Trends in Biochemical Sciences|volume=29|issue=4|pages=210–9|pmid=15082315|url=http://www.phy.ohiou.edu/~braslavs/Biophysics/Articles/Ghanim/ip3receptors.pdf|access-date=2017-10-27|archive-date=2017-08-08|archive-url=https://web.archive.org/web/20170808142233/http://www.phy.ohiou.edu/%7Ebraslavs/Biophysics/Articles/Ghanim/ip3receptors.pdf|url-status=dead}}</ref>