Lsr (AI-2) cell signaling system
Responsible: Kelly Davis, Xiao Zhu
Signal molecule: AI-2 (furanosyl borate diester in V. harveyi, a variety of other molecules in other species), all are derived from DPD. AI-2 is R-THMF in E. coli
lsrA,B,C,D,F,G,R,K: Escherichia coli HS, SMS-3-5, str. K12 substr. MG1655, and substr. DH10B.
lsrE:Escherichia coli str. K12 substr. MG1655
LuxS:Escherichia coli HS, SMS-3-5, APEC O1, str. K12 substr. MG1655, substr. DH10B, and UTI89.
Receiver protein: LsrR protein receives signal from sensor protein
Signal molecule synthase: Pfs enzyme, then LuxS autoinducer synthase
Target genes: lsr operon, including ABC transporter and LsrK kinase
Regulation: LsrR represses the lsr operon, derepression by phospho-AI-2; catabolite repression influences AI-2 accumulation through the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex, which directly stimulates transcription of the lsr operon and indirectly represses luxS expression.cAMP-CRP is shown to bind to a cAMP receptor protein (CRP) binding site located in the upstream region of the lsr promoter and works with the LsrR repressor to regulate AI-2 uptake.
Note: AI-2 is synthesized and secreted during exponential growth and is imported in stationary phase when glucose becomes limiting. In the presence of glucose, AI-2 is not imported because the lsr operon is not transcribed due to camp-CAP mediated repression. Both glycerol and G3P(glycerol 3-phosphate) repress lsr transcription, while the majority repression comes from G3P. DHAP represses lsr transcription by a cAMP-CAP-independent mechanism involving LsrR.
Pfs enzyme (?)
lsrB encodes the periplasmic AI-2 binding protein
lsrC & lsrD encode the channel proteins
lsrA encodes the ATPase that provides energy for AI-2 transport
lsrF is similar to genes specifying aldolases
lsrG encodes a protein with an unknown function.
DHAP: dihydroxyacetone phosphate.
Transcription of LuxS (interaction with micA,gshA)