hutU (PA5100, Q9HU83) review notes

Sources and research (2026-11-05)

No deep-research provider was available; this is manual research. Sources read: the
UniProt record (Swiss-Prot, HAMAP MF_00577), the GOA file, cached PMID:4290562 (abstract
only; the MCP returned no PMC body), PMID:16475788 and the sibling hut reviews in
genes/PSEAE/hutH, hutI and hutF, whose notes record a full-text reading of PMID:4290562.

HutU is urocanase (urocanate hydratase, EC 4.2.1.49), the NAD+-containing enzyme of
step II of histidine degradation, converting trans-urocanate to 4-imidazolone-5-propanoate
(UniProt CC:CATALYTIC ACTIVITY and CC:COFACTOR, HAMAP-Rule MF_00577).
The first three pathway steps are HutH, HutU and HutI
PMID:16475788.
Lessie and Neidhardt 1967 assay urocanase in P. aeruginosa and describe urocanase-deficient
mutants PMID:4290562.
The hutI and hutF notes record that the full text has
these mutants (a copy supplied by the user was read): "Its mutants are a urocanase-deficient strain, a histidine auxotroph and
regulatory mutants with altered repression" (genes/PSEAE/hutI/hutI-notes.md).
The paper predates gene cloning, so the tie between the mutant and PA5100 is an
inference. It is secure: a live UniProt query (2026-11-05, organism_id 208964 with family
urocanase or Pfam PF01175) returns one protein, Q9HU83 hutU PA5100. The phenotype of the
urocanase-deficient mutant (it still induces enzymes I and IV, so it is not a regulatory
mutant) fits a structural-gene lesion.

PseudoCAP IBA-seed assessment

Seeds of PTN002639709 (.cache/paint/IBD.gaf, column 8): GO:0016153 is seeded by
Q96N76 (human UROC1), Q9HU83 (this gene) and P25503 (B. subtilis HutU); GO:0006548 by
Q96N76 and Q9HU83. QuickGO (2026-11-05): UROC1 has GO:0016153 IDA and GO:0006548 IMP
(BHF-UCL, PMID:19304569); B. subtilis HutU has GO:0016153 EXP (UniProt, PMID:4990470).

PTN node	node term	n_seeds	leaf IBAs	seed annotation (term, evidence, PMID)	verdict	rationale	other seeds	IBD stands without this seed?
PTN002639709	GO:0016153 urocanate hydratase activity	3	50 (47 taxa)	GO:0016153 urocanate hydratase activity, IMP, PMID:4290562 (PseudoCAP)	SOUND	The paper assays urocanase and describes a urocanase-deficient mutant; PA5100 is the only urocanase-family protein in PAO1, so loss of the activity maps to this gene. The node term suits a conserved single-function urocanase family (HAMAP MF_00577, TIGR01228). Gene assignment is by inference (pre-cloning paper).	Human UROC1 (IDA), B. subtilis HutU (EXP)	Yes. No GO_CENTRAL defect.
PTN002639709	GO:0006548 L-histidine catabolic process	2	50 (47 taxa)	GO:0006548 L-histidine catabolic process, IMP, PMID:4290562 (PseudoCAP)	SOUND	Urocanase catalyses step II of histidine degradation, named as such in the abstract.	Human UROC1 (IMP, urocanic aciduria)	Yes. No GO_CENTRAL defect.

Consistency with the sibling hut reviews: the same 1967 paper is SOUND for hutH (histidase
assayed directly) and UNVERIFIABLE/MISCITED for hutI and hutF (their steps are not studied).
HutU is in the hutH situation: step II is assayed and a urocanase mutant is described, so the
reference fits this gene. No hut nodes are shared (hutH PTN000796617/PTN000796665, hutI
PTN000505272, hutF PTN000138516, hutU PTN002639709).

Annotation decisions

GO:0016153 (IBA, IEA, IMP): ACCEPT; core activity.
GO:0006548 (IBA, IEA, IMP): ACCEPT; HutU performs step II. As in the sibling reviews, the
general histidine-catabolism term is kept (the urocanase step is shared by the
formamide and formate branches).
GO:0005737 cytoplasm (IEA): ACCEPT; soluble enzyme without signal peptide or TM segment.