Gene Description

PurH is the bifunctional enzyme that completes de novo IMP synthesis. Its AICAR transformylase domain forms FAICAR using 10-formyltetrahydrofolate, and its IMP cyclohydrolase domain closes the purine ring to form IMP.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0003937 IMP cyclohydrolase activity	IEA GO_REF:0000120	ACCEPT	Summary: Correct enzyme-specific molecular function. Reason: The exact Bifunctional purine biosynthesis protein PurH product assignment supports this activity.
GO:0004643 phosphoribosylaminoimidazolecarboxamide formyltransferase activity	IEA GO_REF:0000120	ACCEPT	Summary: Correct enzyme-specific molecular function. Reason: The exact Bifunctional purine biosynthesis protein PurH product assignment supports this activity.
GO:0005829 cytosol	IEA GO_REF:0000118	KEEP AS NON CORE	Summary: Plausible electronic localization that is not core to either catalytic activity. Reason: Cytosol is consistent with a soluble bacterial metabolic enzyme, but no direct localization evidence was found.
GO:0006164 purine nucleotide biosynthetic process	IEA GO_REF:0000002	MODIFY	Summary: Correct but broader than the specific pathway assignment. Reason: Replace the broad purine-nucleotide process with de novo IMP biosynthesis. Proposed replacements: 'de novo' IMP biosynthetic process
GO:0006189 'de novo' IMP biosynthetic process	IEA GO_REF:0000120	ACCEPT	Summary: Correct pathway assignment. Reason: This enzyme catalyzes a required reaction between PRPP and IMP.

Core Functions

Forms FAICAR in the penultimate reaction of de novo IMP synthesis.

Molecular Function:

phosphoribosylaminoimidazolecarboxamide formyltransferase activity

Directly Involved In:

'de novo' IMP biosynthetic process

Supporting Evidence:

file:PSEPK/purH/purH-uniprot.txt
Reaction=(6R)-10-formyltetrahydrofolate + 5-amino-1-(5-phospho-beta-D-
file:PSEPK/purH/purH-uniprot.txt
DR HAMAP; MF_00139; PurH; 1.
file:PSEPK/purH/purH-uniprot.txt
DR NCBIfam; TIGR00355; purH; 1.

Closes the purine ring to form IMP in the terminal reaction.

Molecular Function:

IMP cyclohydrolase activity

Directly Involved In:

'de novo' IMP biosynthetic process

Supporting Evidence:

file:PSEPK/purH/purH-uniprot.txt
Reaction=IMP + H2O = 5-formamido-1-(5-phospho-D-ribosyl)imidazole-4-
file:PSEPK/purH/purH-uniprot.txt
The IMP cyclohydrolase activity resides in the N-terminal region.
file:PSEPK/purH/purH-uniprot.txt
DR HAMAP; MF_00139; PurH; 1.

References

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Suggested Experiments

Experiment: Test a clean purH deletion for purine auxotrophy and rescue by the appropriate downstream purine intermediate or by gene complementation.

📚 Additional Documentation

Notes

(purH-notes.md)

purH curation notes

UniProt identifies Q88DK3 as Bifunctional purine biosynthesis protein PurH [file:PSEPK/purH/purH-uniprot.txt "RecName: Full=Bifunctional purine biosynthesis protein PurH"].
Retain both active-site functions, AICAR transformylase and IMP cyclohydrolase, as
separate core functions. Replace the broad purine nucleotide process with
GO:0006189.

purH