# Autoinducer-2 > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Autoinducer-2 > Markdown URL: https://mediated.wiki/source/Autoinducer-2.md > Source: https://en.wikipedia.org/wiki/Autoinducer-2 > Source revision: 1345030754 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 458783070 | Name = Autoinducer-2 | ImageFile = AI-2.png | ImageSize = 250px | ImageName = Autoinducer-2 | PIN = (3a''S'',6''S'',6a''R'')-2,2,6,6a-Tetrahydroxy-3a-methyltetrahydro-2''H''-furo[2,3-''d''][1,3,2]dioxaborol-2-uide | OtherNames = Dihydroxy[(2S,3R,4S)-2-methyldihydro- |Section1={{Chembox Identifiers | CASNo = | Abbreviations = AI-2 | ChEMBL = 1230903 | KEGG = C16421 | PubChem = 446576 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 393894 | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEBI = 40646 | SMILES = O[C@@H]1[C@]2(O[B-](O[C@]2(OC1)C)(O)O)O | InChI = 1/C5H10BO7/c1-4-5(8,3(7)2-11-4)13-6(9,10)12-4/h3,7-10H,2H2,1H3/q-1/t3-,4+,5+/m0/s1 | InChIKey = ACKRRKSNOOISSG-VPENINKCBL | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C5H10BO7/c1-4-5(8,3(7)2-11-4)13-6(9,10)12-4/h3,7-10H,2H2,1H3/q-1/t3-,4+,5+/m0/s1 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = ACKRRKSNOOISSG-VPENINKCSA-N }} |Section2={{Chembox Properties | Formula = C5H10BO7 | MolarMass = 192.940 | Appearance = | Density = | MeltingPt = | BoilingPt = | Solubility = }} |Section3={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }} '''Autoinducer-2''' ('''AI-2''') is a furanosyl [borate diester](/source/borate_ester) or tetrahydroxy furan (species dependent) that—as the name suggests—is an [autoinducer](/source/autoinducer), a member of a family of [signaling molecule](/source/signaling_molecule)s used in [quorum sensing](/source/quorum_sensing).{{Cite journal| last1= Cao | first1= Jie-Gang | last2= Meighen | first2= Edward A. | year= 1989 | title= Purification and structural identification of an autoinducer for the luminescence system of Vibrio harveyi | journal= [Journal of Biological Chemistry](/source/Journal_of_Biological_Chemistry) | volume= 264 | issue= 36 | pages= 21670–21676 | doi= 10.1016/S0021-9258(20)88238-6 | pmid= 2600086 | doi-access= free }} AI-2 is one of only a few known [biomolecules](/source/biomolecules) incorporating [boron](/source/boron). First identified in the [marine bacterium](/source/marine_bacterium) ''[Vibrio harveyi](/source/Vibrio_harveyi)'', AI-2 is produced and recognized by many [Gram-negative](/source/Gram-negative) and [Gram-positive bacteria](/source/Gram-positive_bacteria).{{Cite journal| doi= 10.1016/j.molcel.2004.07.020| last1= Miller | first1= Stephen T. | last2= Xavier | first2= Karina B. | last3= Campagna | first3= Shawn R. | last4= Taga | first4= Michiko E. | last5= Semmelhack | first5= Martin F. | last6= Bassler | first6= Bonnie L. | last7= Hughson | first7= Frederick M. | year= 2004 | title= Salmonella typhimurium Recognizes a Chemically Distinct Form of the Bacterial Quorum-Sensing Signal AI-2 | journal= [Molecular Cell](/source/Molecular_Cell) | volume= 15 | issue= 5 | pages= 677–687 | pmid= 15350213 | doi-access= free }}{{Cite journal| doi= 10.1146/annurev.micro.55.1.165| last1= Miller | first1= M. B. | last2= Bassler | first2= B. L. | year= 2001 | title= Quorum sensing in bacteria | journal= [Annual Review of Microbiology](/source/Annual_Review_of_Microbiology) | volume= 55 | pages= 165–199 | pmid= 11544353 }} AI-2 arises by the reaction of [4,5-dihydroxy-2,3-pentanedione](/source/4%2C5-Dihydroxy-2%2C3-pentanedione), which is produced enzymatically, with [boric acid](/source/boric_acid){{Cite web|url=http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/misc/AI2.html|title = Chemistry - Queen Mary University of London}} and is recognized by the two-component sensor kinase LuxPQ in [Vibrionaceae](/source/Vibrionaceae). AI-2 is actively transported by the Lsr ABC-type transporter into the cell in [Enterobacteriaceae](/source/Enterobacteriaceae) and few other bacterial taxa such as ''[Pasteurella](/source/Pasteurella)'', ''[Photorhabdus](/source/Photorhabdus)'', ''[Haemophilus](/source/Haemophilus)'', and ''[Bacillus](/source/Bacillus)'',{{cite journal|last1=Rezzonico|first1=F.|last2=Smits|first2=T.H.M.|last3=Duffy|first3=B.|title=Detection of AI-2 receptors in genomes of Enterobacteriaceae suggests a role of type-2 quorum sensing in closed ecosystems|journal=Sensors|date=2012|volume=12|issue=5|pages=6645–6665|doi=10.3390/s120506645|pmc=3386761|pmid=22778662|bibcode=2012Senso..12.6645R|doi-access=free}} where it is phosphorylated by [LsrK](/source/LsrK). Then, Phospho-AI-2 binds the transcriptional repressor protein, LsrR, which subsequently is released from the promoter/operator region of the lsr operon – and transcription of the ''lsr'' genes is initiated. AI-2 signalling is also regulated by glucose and cAMP/CRP via the ''lsr'' operon. In the presence of glucose, low levels of cAMP/CRP result in almost no ''lsr'' operon (''lsrABCDFG'') expression. Without glucose, cAMP-CRP is needed to stimulate the ''lsr'' expression, while LsrR represses its expression in the absence of the inducer, phospho-AI-2. As AI-2 accumulates, more AI-2 is taken in via LsrABCD, phosphorylated via LsrK, and the ''lsr'' transcription is de-repressed, enabling even more AI-2 uptake.{{Cite journal| doi= 10.1128/JB.187.6.2066-2076.2005| last1= Wang | first1= Liang | last2= Hashimoto | first2= Yoshifumi | last3= Tsao | first3= Chen-Yu | last4= Valdes | first4= James J. | last5= Bentley | first5= William E. | year= 2005 | title= Cyclic AMP (cAMP) and cAMP Receptor Protein Influence both Synthesis and Uptake of Extracellular Autoinducer 2 in Escherichia coli | journal= [Journal of Bacteriology](/source/Journal_of_Bacteriology) | volume= 187 | issue= 6 | pages= 2066–2076 | pmid= 15743955| pmc= 1064054 }} Doubts have been expressed regarding AI-2's status as a universal signal. Although the ''luxS'' gene, which encodes the protein responsible for AI-2 production is widespread, the latter has mainly a primary metabolic role in the recycling of [''S''-adenosyl-L-methionine](/source/S-Adenosyl_methionine), with AI-2 being a by-product of that process.{{Cite journal | last1 = Diggle | first1 = S. P. | last2 = Gardner | first2 = A. | last3 = West | first3 = S. A. | last4 = Griffin | first4 = A. S. | title = Evolutionary theory of bacterial quorum sensing: when is a signal not a signal? | journal = Philosophical Transactions of the Royal Society B: Biological Sciences | volume = 362 | issue = 1483 | pages = 1241–1249 | year = 2007 | doi = 10.1098/rstb.2007.2049 | pmid=17360270 | pmc=2435587}} An unequivocally AI-2 related behavior was found to be restricted primarily to organisms bearing known AI-2 receptor genes.{{cite journal|last1=Rezzonico|first1=F.|last2=Duffy|first2=B.|title=Lack of genomic evidence of AI-2 receptors suggests a non-quorum sensing role for luxS in most bacteria|journal=BMC Microbiology|date=2008|volume=8|page=154|pmid=18803868|doi=10.1186/1471-2180-8-154|pmc=2561040 |doi-access=free }} Thus, while it is certainly true that some bacteria respond to AI-2, it is doubtful that it is always being produced for purposes of signaling. == Mimicry by host cells == It has been found that in response to bacteria or to disruption of the [tight junction](/source/tight_junction), [mammalian](/source/mammal) [epithelial](/source/epithelium) cells synthesize an AI-2 mimic that triggers quorum sensing and may play an important role in enlisting gut microbes that are known to assist in epithelial healing. In reporting these findings, the researchers write that their results “suggest that [crosskingdom](/source/kingdom_(biology)) communication occurs between [eukaryotic](/source/eukaryotic) cells and bacteria via the AI-2 bacterial quorum-sensing system.” {{cite journal |last1=Ismail |first1=Anisa S. |last2=Valastyan |first2=Julie S. |last3=Bassler |first3=Bonnie L. |date=March 17, 2016 |title= A Host-Produced Autoinducer-2 Mimic Activates Bacterial Quorum Sensing |journal=Cell Host & Microbe |volume=19 |issue=4 |pages=470–480 |doi=10.1016/j.chom.2016.02.020 |pmid=26996306 |pmc=4869860 }} == References == {{Reflist}} Category:Signal transduction Category:Cell biology Category:Cell communication Category:Tetrahydroxyborate esters Category:Boron heterocycles Category:Furans Category:Heterocyclic compounds with 2 rings --- Adapted from the Wikipedia article [Autoinducer-2](https://en.wikipedia.org/wiki/Autoinducer-2) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Autoinducer-2?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.