CyaB (PA3217) is the principal adenylyl cyclase of Pseudomonas aeruginosa, a class IIIb nucleotidyl cyclase that converts ATP to cAMP. An N-terminal MASE2 (membrane-associated sensor 2) domain with six predicted transmembrane helices anchors the protein in the cytoplasmic (inner) membrane and is required for full activity in vivo; the C-terminal cytoplasmic catalytic domain needs a divalent cation and is stimulated by CO2/bicarbonate, as in other class IIIb enzymes. CyaB accounts for most intracellular cAMP. Its activity is controlled by the Chp chemosensory system, and the cAMP it makes binds the CRP-family transcription factor Vfr, which globally activates host-directed virulence genes, including the type III secretion system and type IV pili. cyaB mutants are attenuated in a mouse pneumonia model.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: Class III adenylyl cyclases use two divalent metal ions (Mg2+ or Mn2+) at the active site; CyaB activity was measured with either cation. Reason: Cofactor binding that supports catalysis; true but not the core function. Supporting Evidence: PMID:22226839 CO2/HCO3β stimulated CyaB217β463 activity in the presence of either divalent, with optimal stimulation occurring at pH 7. |
| GO:0004016 adenylate cyclase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002454020 with 12 seeds: eleven IDA seeds (M. tuberculosis Rv1264/Rv1318c/Rv1319c/Rv1647, six T. brucei receptor ACs, Dictyostelium AcrA) and the PseudoCAP IMP on CyaB itself (expected, not circular). Reason: Core activity, directly shown for purified CyaB. Supporting Evidence: PMID:22226839 CO2/HCO3β stimulated CyaB217β463 activity in the presence of either divalent, with optimal stimulation occurring at pH 7. |
| GO:0004016 adenylate cyclase activity | IMP PMID:12586068 Coordinate regulation of bacterial virulence genes by a nove... | ACCEPT | Summary: PseudoCAP seed row. The abstract describes mutants unable to make cAMP and a membrane-associated adenylate cyclase; the activity is confirmed with purified enzyme in PMID:22226839. Reason: Seed verdict SOUND; the term is correct for CyaB. Supporting Evidence: PMID:12586068 led to the identification of a signaling pathway that originates from a membrane-associated adenylate cyclase and controls TTSS gene expression |
| GO:0006171 cAMP biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN002454020; three M. tuberculosis IDA seeds plus CyaB. Reason: The enzyme catalyses the single step of cAMP synthesis. Supporting Evidence: PMID:22226839 CyaB activity indeed accounts for the majority of intracellular cAMP |
| GO:0006171 cAMP biosynthetic process | IMP PMID:12586068 Coordinate regulation of bacterial virulence genes by a nove... | ACCEPT | Summary: PseudoCAP seed row; mutants lacking cAMP synthesis. Reason: Seed verdict SOUND; CyaB makes most cellular cAMP. Supporting Evidence: PMID:12586068 Transcriptome analysis of mutants lacking the ability to synthesize cAMP or the cAMP binding protein Vfr |
| GO:0009190 cyclic nucleotide biosynthetic process | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO from the nucleotide cyclase domain. Reason: Entailed by GO:0006171 cAMP biosynthetic process (is_a), accepted above. |
| GO:0009975 cyclase activity | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA generic term. Reason: Entailed by GO:0004016 (is_a GO:0009975), accepted above. |
| GO:0016849 phosphorus-oxygen lyase activity | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA generic term. Reason: Entailed by GO:0004016 (is_a GO:0016849), accepted above. |
| GO:0035556 intracellular signal transduction | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: CyaB generates the second messenger cAMP that signals through Vfr. The more specific GO:0019933 cAMP-mediated signaling is obsolete, so this is as precise as the ontology now allows for a bacterial cAMP pathway. Reason: True (second-messenger production is part of the Chp-CyaB-cAMP-Vfr signalling route) but the gene's core role is the enzymatic step. Supporting Evidence: PMID:12586068 led to the identification of a signaling pathway that originates from a membrane-associated adenylate cyclase and controls TTSS gene expression |
| GO:0005886 plasma membrane | IDA PMID:22226839 Crystal structure and regulation mechanisms of the CyaB aden... | NEW | Summary: Proposed. Full-length CyaB fractionates exclusively with total and inner membranes; removing the MASE2 domain makes it soluble. Six predicted TM helices agree. Reason: Direct fractionation evidence for inner (cytoplasmic) membrane location, consistent with the MASE2 topology. Supporting Evidence: PMID:22226839 Full-length CyaB and CyaBΞ1β17 were detected exclusively in the total membrane and inner membrane fractions |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: What signal does the MASE2 domain sense, and how does the Chp chemosensory system (via surface contact) modulate CyaB activity?
Experiment: Reconstitute full-length CyaB in proteoliposomes and test whether Chp pathway components or surface-contact signals alter cyclase activity.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)