GacS is a membrane-associated hybrid sensor histidine kinase of the GacS/GacA global regulatory system. Its domain architecture indicates a two-pass inner-membrane sensor with HAMP, histidine kinase, receiver, and HPt domains, consistent with multistep phosphorelay signaling. In Pseudomonas putida KT2440, genetic studies link GacS to broad lifestyle control, including surface attachment and positive regulation of the K1 type VI secretion system, so its core role is signal sensing and phosphorelay rather than a pathway-specific metabolic function.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000155 phosphorelay sensor kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the best existing molecular-function annotation for GacS. UniProt and domain architecture identify a membrane-bound hybrid sensor histidine kinase with histidine kinase, receiver, and HPt modules, exactly the architecture expected for a phosphorelay sensor kinase. Reason: GO:0000155 captures the core biochemical role of GacS more precisely than the generic parent terms for histidine kinase or phosphorus-group transferase activity. Supporting Evidence: UniProt:Q88MC3 -!- CATALYTIC ACTIVITY: Reaction=ATP + protein L-histidine = ADP + protein N-phospho-L- histidine.; EC=2.7.13.3; Evidence={ECO:0000256|ARBA:ARBA00000085}; file:PSEPK/gacS/gacS-notes.md The core molecular role is phosphorelay sensor kinase activity at the membrane. |
| GO:0004673 protein histidine kinase activity | IEA GO_REF:0000003 | MARK AS OVER ANNOTATED | Summary: GacS does perform protein histidine kinase chemistry, but this annotation is less informative than GO:0000155 for a hybrid sensory phosphorelay protein. The sensor-kinase context is the biologically important distinction here. Reason: This parent term is biochemically correct but redundant once GO:0000155 phosphorelay sensor kinase activity is present. |
| GO:0016772 transferase activity, transferring phosphorus-containing groups | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This is a very broad ancestral parent of histidine kinase activity. It does not add useful information beyond the much more specific phosphorelay sensor kinase annotation already present. Reason: The term is correct only at a very high level and should not be treated as a core annotation for a well-characterized hybrid sensor kinase. |
| GO:0000160 phosphorelay signal transduction system | IEA GO_REF:0000002 | ACCEPT | Summary: This is the correct process-level abstraction for GacS. In KT2440, GacS is part of the GacS/GacA phosphorelay that controls downstream programs such as surface attachment and K1 type VI secretion system expression. Reason: GacS is a membrane hybrid sensor kinase whose core biological role is initiating phosphorelay signaling, with adhesion and secretion phenotypes representing downstream outputs of that regulatory cascade. Supporting Evidence: file:PSEPK/gacS/gacS-notes.md Process terms should center on phosphorelay signal transduction; the documented adhesion and T6SS phenotypes are downstream outputs of that global signaling role rather than separate direct molecular activities. file:PSEPK/gacS/gacS-notes.md In KT2440, expression of the K1 type VI secretion system gene cluster is positively regulated by the GacS-GacA two-component system and repressed by RetS. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: GacS certainly participates in signal transduction, but GO:0007165 is too broad for a protein whose signaling mode is already captured by GO:0000160 phosphorelay signal transduction system. Reason: The more specific phosphorelay term should carry the biology here; the generic parent adds little value. |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: GacS is a transmembrane sensor located in the bacterial inner membrane. In bacterial GO usage, plasma membrane is the appropriate cellular-component term for this localization. Reason: Membrane localization is essential to GacS function because it senses external/periplasmic cues and transmits them through a membrane-embedded signaling architecture. Supporting Evidence: UniProt:Q88MC3 -!- SUBCELLULAR LOCATION: Cell inner membrane {ECO:0000256|ARBA:ARBA00004429}; Multi-pass membrane protein {ECO:0000256|ARBA:ARBA00004429}. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: This term is correct but unnecessarily general because the protein is already localized more specifically to the plasma membrane. Reason: GO:0005886 plasma membrane is the more informative and appropriate cellular-component annotation for GacS. |
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Download this section (compressed HTML)Q: What signal or signals are detected directly by the periplasmic sensor region of GacS in KT2440?
Suggested experts: Patricia Bernal, María A. Llamas
Q: Which small RNAs and Rsm-family effectors mediate the adhesion versus K1-T6SS branches downstream of GacS/GacA in KT2440?
Suggested experts: Patricia Bernal, Estrella Duque, Juan-Luis Ramos
Experiment: Build phosphosite mutants in the predicted receiver Asp718 and HPt His863 modules, then test phosphotransfer to GacA in vitro and with in vivo transcriptional reporters for Gac-dependent outputs.
Hypothesis: GacS uses its hybrid receiver and HPt modules to relay phosphate to GacA in a defined multistep order.
Type: phosphotransfer biochemistry plus reporter genetics
Experiment: Compare RNA-seq and promoter-reporter responses in wild type, delta-gacS, and sensor-domain or relay-module mutants during surface growth and stationary phase to separate direct GacS outputs from secondary physiological effects.
Hypothesis: The adhesion and K1-T6SS outputs reflect distinct downstream branches of the same GacS/GacA signaling pathway.
Type: comparative transcriptomics and promoter-reporter analysis
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