LuxS is the cytosolic S-ribosylhomocysteine lyase of the bacterial activated methyl cycle. It cleaves S-ribosylhomocysteine to L-homocysteine and 4,5-dihydroxy-2,3-pentadione, regenerating homocysteine for methionine recycling and producing the precursor that spontaneously cyclizes to the AI-2 quorum-sensing signal.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005506 iron ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: The family-level InterPro inference that LuxS binds iron is consistent with the conserved LuxS metalloenzyme fold. Reason: LuxS-family S-ribosylhomocysteine lyases use a divalent metal center, and UniProt records this E. coli enzyme as binding one Fe cation per subunit. The cofactor binding is real but supports the catalytic lyase activity rather than constituting a separate core molecular function. |
| GO:0005515 protein binding | IPI PMID:15690043 Interaction network containing conserved and essential prote... | REMOVE | Summary: The DnaK interaction comes from a large-scale affinity-purification/mass spectrometry network and does not identify a specific LuxS activity. Reason: The reported physical interaction is not evidence for a narrower molecular function than the low-information parent term protein binding, and LuxS is a metabolic lyase rather than a DnaK co-chaperone or dedicated adaptor. Supporting Evidence: PMID:15690043 affinity-tagged alleles of 1,000 open reading frames (approximately 23% of the genome) |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: The PAINT cytosol assertion fits the soluble, cytosolic activated methyl cycle chemistry performed by LuxS. Reason: LuxS has its own curated cytosol evidence in E. coli and belongs to a bacterial S-ribosylhomocysteine lyase clade whose activity is inherited from the same cytosolic state; the target's presence in the IBA WITH/FROM is expected because target-specific evidence helped seed the PAINT node. |
| GO:0005829 cytosol | IDA PMID:15911532 Localization, annotation, and comparison of the Escherichia ... | ACCEPT | Summary: EcoCyc curated LuxS to the cytosol from an E. coli biochemical fractionation and tandem-MS proteome survey. Reason: The localization is consistent with LuxS being a soluble enzyme of the bacterial activated methyl cycle, and the experimental source separated E. coli proteins into cytosolic, periplasmic, inner-membrane, and outer-membrane fractions. Supporting Evidence: PMID:15911532 2,160 were annotated and assigned to the cytosol, periplasm, inner membrane, and outer membrane by biochemical fractionation followed by two-dimensional gel electrophoresis and tandem mass spectrometry |
| GO:0005829 cytosol | IDA PMID:18304323 Protein abundance profiling of the Escherichia coli cytosol. | ACCEPT | Summary: EcoCyc curated a second cytosolic localization for LuxS from a shotgun E. coli cytosol proteomics study. Reason: This IDA row agrees with the independent cytosol assignment above and with the lack of membrane or secretion features in LuxS. Supporting Evidence: PMID:18304323 Using a combination of LC-MS/MS approaches with protein and peptide fractionation steps we identified 1103 proteins from the cytosolic fraction of the Escherichia coli strain MC4100. |
| GO:0009372 quorum sensing | IEA GO_REF:0000120 | ACCEPT | Summary: Automated UniProt rules correctly associate LuxS-family enzymes with AI-2 quorum-sensing signal biosynthesis. Reason: LuxS participates in quorum sensing by generating 4,5-dihydroxy-2,3-pentadione, the precursor that yields AI-2 signal molecules; this process role is a direct consequence of its S-ribosylhomocysteine lyase activity. |
| GO:0009372 quorum sensing | IMP PMID:11514505 DNA microarray-based identification of genes controlled by a... | ACCEPT | Summary: An E. coli luxS mutant unable to synthesize AI-2 was used to define AI-2-responsive transcription. Reason: Loss of luxS blocks synthesis of the AI-2 signal and thereby places LuxS upstream of the quorum-sensing response. LuxS performs the AI-2 producer step rather than signal detection, but production of the extracellular signal is part of the quorum-sensing process. Supporting Evidence: PMID:11514505 We investigated global changes in mRNA abundance elicited by the AI-2 signaling molecule through the use of a luxS mutant that was unable to synthesize AI-2. |
| GO:0043768 S-ribosylhomocysteine lyase activity | IBA GO_REF:0000033 | ACCEPT | Summary: The PAINT inference captures the family-defining LuxS activity at the correct level of specificity. Reason: E. coli LuxS is experimentally supported as an S-ribosylhomocysteine lyase, and there is no evidence of target-specific loss or divergence that would challenge the PAINT node placement. |
| GO:0043768 S-ribosylhomocysteine lyase activity | IDA PMID:11489131 The LuxS family of bacterial autoinducers: biosynthesis of a... | ACCEPT | Summary: Schauder et al. directly established the LuxS substrate and products in the AI-2 biosynthetic pathway. Reason: The paper identifies LuxS as the enzyme that cleaves S-ribosylhomocysteine to homocysteine plus the AI-2 precursor/product, exactly matching GO:0043768. Supporting Evidence: PMID:11489131 The substrate for LuxS is S-ribosylhomocysteine, which is cleaved to form two products, one of which is homocysteine, and the other is AI-2. |
| GO:0043768 S-ribosylhomocysteine lyase activity | IEA GO_REF:0000120 | ACCEPT | Summary: RHEA, EC, InterPro, and UniRule all point to the experimentally verified LuxS S-ribosylhomocysteine lyase activity. Reason: The automated assertion is specific and is corroborated by the experimental E. coli annotation and the PAINT family assertion for the same activity. |
| GO:0043768 S-ribosylhomocysteine lyase activity | ISS PMID:9990077 Quorum sensing in Escherichia coli, Salmonella typhimurium, ... | ACCEPT | Summary: The E. coli and Vibrio harveyi luxS genes encode homologous AI-2 production proteins. Reason: The sequence-similarity assertion is consistent with the original cross-species identification of luxS as an AI-2 production gene family and with the later direct E. coli biochemical annotation. Supporting Evidence: PMID:9990077 Here we report the identification and analysis of the gene responsible for AI-2 production in V. harveyi, S. typhimurium, and E. coli. |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | MODIFY | Summary: This broad InterPro metal-binding call is directionally correct but less specific than the existing iron ion binding annotation. Reason: LuxS is a metal-dependent S-ribosylhomocysteine lyase with one inferred Fe cation per subunit, so GO:0005506 captures the cofactor more precisely than generic metal ion binding. Proposed replacements: iron ion binding |
| GO:0033353 L-methionine cycle | IDA PMID:11489131 The LuxS family of bacterial autoinducers: biosynthesis of a... | NEW | Summary: LuxS directly releases homocysteine from S-ribosylhomocysteine in the bacterial two-step SAH-processing route of the activated methyl cycle. Reason: LuxS catalyzes the second MtnN/Pfs-LuxS route step, producing L-homocysteine that can be remethylated to regenerate L-methionine after SAM-dependent methyl transfer. Supporting Evidence: PMID:11489131 We show here that LuxS is the AI-2 synthase and that AI-2 is produced from S-adenosylmethionine in three enzymatic steps. |
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