LuxS: its role in central metabolism and the in vitro synthesis of 4-hydroxy-5-methyl-3(2H)-furanone

Abstract

Many bacteria produce extracellular molecules which function in cell-to-cell communication. One of these molecules, autoinducer 2 (AI-2), was first described as an extracellular signal produced by Vibrio harveyi to control luciferase expression. Subsequently, a number of bacteria have been shown to possess AI-2 activity in their culture supernatants, and bear the luxS gene product, which is required for AI-2 synthesis. In Porphyromonas gingivalis, luxS and pfs, encoding a 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTA/SAH'ase), form an operon, suggesting that Sadenosylhomocysteine (SAH) or 5'-methylthioadenosine (MTA) serves as a substrate for AI-2 production. Cell-free extracts of Escherichia coli MG1655, but not DH5α (which carries a luxS frame-shift mutation) were capable of generating AI-2 activity upon addition of SAH, but not MTA. S-Ribosylhomocysteine (RH) derived from SAH also served as a substrate in E. coli MG1655 extracts. RH-supplemented cell-free extracts of Pseudomonas aeruginosa, a bacterium that lacks luxS, only generated AI-2 activity following the introduction of a plasmid containing the Por. gingivalis pfs-luxS operon. In addition, defined in vitro systems consisting of the purified LuxS proteins from Por. gingivalis, E. coli, Neisseria meningitidis or Staphylococcus aureus converted RH to homocysteine and a compound that exhibits AI-2 activity. 4-Hydroxy-5-methyl-3(2H)-furanone was identified by mass spectrometry analysis as a major product formed in this in vitro reaction. In E. coli MG1655, expression of T3SH [the bacteriophage T3 S-adenosylmethionine (SAM) hydrolase] significantly reduced AI-2 activity in culture supernatants, suggesting that AI-2 production is limited by the amount of SAH produced in SAM-dependent transmethylase reactions. The authors suggest that the LuxS protein has an important metabolic function in the recycling of SAH. They also show that Ps. aeruginosa is capable of removing AI-2 activity, implying that this molecule may act as a nutrient. In many bacteria AI-2 may in fact represent not a signal molecule but a metabolite which is released early and metabolized in the later stages of growth.

LsrR-binding site recognition and regulatory characteristics in Escherichia coli AI-2 quorum sensing

“…Since LsrR contains a predicted HTH DNA-binding domain, it has been suggested to repress the transcription of the lsr operon and itself by directly binding to their promoters. In order to determine whether LsrR can bind to the lsrA and lsrR promoter regions, we carried out gel evidence showed that in V. harveyi, AI-2 is (2S, 4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran-borate (S-THMF-borate); and in E. coli and S. typhimurium, AI-2 is (2R, 4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF) [10,[16][17][18][19][20][21][22].…”

“…In every case, AI-2 is synthesized by LuxS, which functions in the pathway for metabolism of S-adenosylmethionine (SAM), a major cellular methyl donor. In a metabolic pathway known as the activated methyl cycle, SAM is metabolized to Sadenosylhomocysteine, which is subsequently converted to adenine, homocysteine, and 4,5-dihydroxy-2,3-pentanedione (DPD, the precursor of AI-2) by the sequential action of the enzymes Pfs and LuxS [10,16]. DPD is a highly reactive product that can rearrange and undergo additional reactions, suggesting that distinct but related molecules derived from DPD may be the signals that different bacterial species recognize as AI-2.…”

Genetic and physiological characterization of the Borrelia burgdorferi ORF BB0374-pfs-metK-luxS operon

“…Other bacteria, B. burgdorferi included, further degrade SRH to DPD and homocysteine via the LuxS enzyme (Babb et al, 2005;Stevenson & Babb, 2002;Stevenson et al, 2003;Sun et al, 2004;Xavier & Bassler, 2003). The majority of bacteria salvage homocysteine for regeneration of methionine, for use in additional transmethylation reactions or protein synthesis (Winzer et al, 2002). B. burgdorferi is among the minority of bacteria which lack methionine synthase, and are therefore unable to utilize the homocysteine produced by LuxS (Babb et al, 2005).…”

Heterologous Expression of sahH Reveals That Biofilm Formation Is Autoinducer-2-independent in Streptococcus sanguinis but Is Associated with an Intact Activated Methionine Cycle

“…1), which provides activated methyl groups for the methylation of DNA, RNA, proteins and other substrates (5,9,12,13). The LuxS/Pfs pathway, which is present in Gamma-, Beta-, and Epsilonproteobacteria as well as in Firmicutes (5), is responsible for the recycling of the toxic intermediate S-adenosylhomocysteine (SAH) to homocysteine.…”