autoinducer-2

{{chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 458783070

| Name = Autoinducer-2

| ImageFile = AI-2.png

| ImageSize = 250px

| ImageName = Autoinducer-2

| PIN = (3aS,6S,6aR)-2,2,6,6a-Tetrahydroxy-3a-methyltetrahydro-2H-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 or tetrahydroxy furan (species dependent) that—as the name suggests—is an autoinducer, a member of a family of signaling molecules used in 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 | 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 incorporating boron. First identified in the marine bacterium Vibrio harveyi, AI-2 is produced and recognized by many Gram-negative and 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 | 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 | volume= 55 | pages= 165–199 | pmid= 11544353 }} AI-2 arises by the reaction of 4,5-dihydroxy-2,3-pentanedione, which is produced enzymatically, with 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.

AI-2 is actively transported by the Lsr ABC-type transporter into the cell in Enterobacteriaceae and few other bacterial taxa such as Pasteurella, Photorhabdus, Haemophilus, and 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. 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 | 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, 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.