PfeE (PA2689) is a periplasmic esterase-D-family (alpha/beta hydrolase fold) siderophore hydrolase of Pseudomonas aeruginosa, encoded next to the ferric-enterobactin outer-membrane transporter gene pfeA and induced, like pfeA, by enterobactin. Purified PfeE hydrolyses the trilactone backbone of ferric enterobactin, a xenosiderophore made by enterobacteria, into three 2,3-dihydroxybenzoylserine units that remain bound to iron; complete release of the iron needs a reductant as well. Crystal structures of PfeE alone and of an inactive mutant bound to ferric enterobactin define the substrate site and a Ser-His-Asp catalytic triad. PfeE is a monomer located in the periplasm, so in P. aeruginosa iron is released from enterobactin in the periplasm, and ferric enterobactin never reaches the cytoplasm (unlike E. coli, where the cytoplasmic esterase Fes does this). Deleting pfeE strongly reduces iron uptake via enterobactin. PfeE can also hydrolyse salmochelin S4.
Definition: Catalysis of the hydrolysis of the three ester bonds of the trilactone backbone of Fe(III)-enterobactin, giving Fe(III)-(2,3-dihydroxybenzoyl-L-serine) and two free 2,3-dihydroxybenzoyl-L-serine molecules (RHEA:30111; EC 3.1.1.108).
Justification: GO:0008849 enterochelin esterase activity is defined on iron-free enterobactin. PfeE (and E. coli Fes) act on the ferric siderophore; no GO term covers EC 3.1.1.108.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016788 hydrolase activity, acting on ester bonds | IBA GO_REF:0000033 | MODIFY | Summary: IBA from PTN002868704 (siderophore esterase clade; 3 seeds, 9 leaf IBAs in 8 taxa). Seeds are Aspergillus fumigatus SidJ (Q4WF29, fusarinine C esterase, AspGD IMP), Aspergillus nidulans EstB (Q5AV79, triacetylfusarinine C esterase, UniProt EXP GO:0008849) and PfeE itself (PseudoCAP IDA, PMID:30086222). Reason: The node term is correct and suitably broad for a clade of siderophore esterases acting on different siderophores, and the IBD would stand on the two Aspergillus seeds. For PfeE the bond hydrolysed is known: the carboxylic ester (lactone) bonds of the enterobactin triserine backbone, so the specific term is GO:0052689 carboxylic ester hydrolase activity (is_a GO:0016788). No GO term exists yet for ferric-enterobactin esterase activity (EC 3.1.1.108); one is proposed. No node-level defect. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002868704 · PTN002868704 SUPPORTS TRANSFER Siderophore esterase node (PTHR40841); generic ester hydrolase term is appropriate for a clade whose members hydrolyse different siderophores; the gene-level term is more specific. UniProtKB:Q4WF29 · A. fumigatus SidJ SUPPORTS TRANSFER AspGD IMP GO:0016788 (PMID:17586718), fusarinine C hydrolysis. UniProtKB:Q5AV79 · A. nidulans EstB SUPPORTS TRANSFER UniProt EXP GO:0008849 (PMID:30070018), a descendant of the node term. UniProtKB:Q9I0F2 · pfeE (self; IDA PMID:30086222) SUPPORTS TRANSFER Expected self-seed reflecting the purified-enzyme evidence. Proposed replacements: carboxylic ester hydrolase activity Supporting Evidence: PMID:30086222 Purified PfeE hydrolyzed ferri-ENT into three molecules of 2,3-DHBS (2,3-dihydroxybenzoylserine) still complexed with ferric iron |
| GO:0016788 hydrolase activity, acting on ester bonds | IDA PMID:30086222 A Key Role for the Periplasmic PfeE Esterase in Iron Acquisi... | MODIFY | Summary: PseudoCAP IDA, the PTN002868704 seed row. Purified PfeE hydrolyses ferric enterobactin into three iron-bound DHBS units. Reason: The abstract states the purified-enzyme hydrolysis of ferric enterobactin directly, so the row is sound; seed verdict SOUND. The term is correct but general: the bonds hydrolysed are carboxylic ester (lactone) bonds, so MODIFY to GO:0052689; a ferric-enterobactin esterase term (EC 3.1.1.108, RHEA:30111) is proposed for the exact reaction. Proposed replacements: carboxylic ester hydrolase activity Supporting Evidence: PMID:30086222 Purified PfeE hydrolyzed ferri-ENT into three molecules of 2,3-DHBS (2,3-dihydroxybenzoylserine) still complexed with ferric iron |
| GO:0042597 periplasmic space | EXP PMID:30086222 A Key Role for the Periplasmic PfeE Esterase in Iron Acquisi... | MODIFY | Summary: UniProt EXP periplasm from cell fractionation and fluorescence microscopy. Reason: Correct; P. aeruginosa is Gram-negative, so its periplasm is the outer membrane-bounded periplasmic space, GO:0030288, an is_a descendant of the annotated term. Proposed replacements: outer membrane-bounded periplasmic space Supporting Evidence: PMID:30086222 cell fractionation and fluorescence microscopy showed periplasmic localization of PfeE in P. aeruginosa cells |
| GO:0042597 periplasmic space | IEA GO_REF:0000044 | MODIFY | Summary: UniProt subcellular-location mapping (Periplasm). Reason: As for the EXP row, the specific Gram-negative term is GO:0030288. Proposed replacements: outer membrane-bounded periplasmic space Supporting Evidence: PMID:30086222 cell fractionation and fluorescence microscopy showed periplasmic localization of PfeE in P. aeruginosa cells |
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Download this section (compressed HTML)Q: Should PfeE carry a process term for siderophore-iron import? Comparable esterases (E. coli Fes, A. fumigatus SidJ) carry GO:0033214 only as acts_upstream_of_or_within from mutant data; is iron release by siderophore hydrolysis a step of import in GO's sense?
Q: Which periplasmic or inner-membrane reductase completes iron release from the Fe(III)-DHBS products of PfeE?
Experiment: Screen periplasmic reductase mutants for loss of enterobactin-dependent 55Fe uptake in a pfeE-proficient background, and assay iron release from PfeE products in periplasmic extracts.
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