YciC (also known as ZagA - ZTP-activated GTPase A) is a zinc metallochaperone that belongs to the COG0523 subfamily of G3E P-loop GTPases and directly transfers zinc cofactor to target proteins. The protein binds zinc with exceptionally high affinity (K_Zn ≥ 10^11 M^-1) and transfers it from its CXCC motif to specific client proteins, particularly FolE (GTP cyclohydrolase IA) that is critical for de novo folate biosynthesis. This represents the first demonstrated physical interaction between a COG0523 metallochaperone and its client protein. The zinc transfer mechanism requires both GTP hydrolysis (stimulated ~5-fold by zinc binding) and activation by the alarmone ZTP (zinc-associated alarmone). Under zinc limitation, declining FolE activity leads to folate deficiency, causing ZMP accumulation and conversion to ZTP, which then activates ZagA to interact with FolE and maintain folate biosynthesis - a sophisticated feedback circuit. YciC/ZagA is regulated by the zinc-sensing metalloregulator Zur and represents a paradigm for understanding metallochaperone function.
Definition: Catalysis of GTP hydrolysis coupled to the direct transfer of zinc ions from a donor CXCC motif to acceptor metalloproteins
Justification: YciC/ZagA and related COG0523 proteins represent a unique class of metallochaperones that couple GTP hydrolysis to zinc transfer, distinct from other chaperones or GTPases.
Definition: Zinc chaperone activity that is specifically activated by the alarmone ZTP (zinc-associated alarmone) during zinc limitation conditions
Justification: ZagA represents the first characterized ZTP-responsive metallochaperone, requiring this alarmone for optimal interaction with client proteins like FolE during zinc starvation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: Too general - more specific as GTP binding for this P-loop GTPase Reason: While accurate, GTP binding is more specific and informative for yciC function. |
| GO:0005525 GTP binding | IEA GO_REF:0000043 | ACCEPT | Summary: Correct - yciC is a P-loop GTPase that requires GTP binding for zinc transfer Reason: Accurately describes the molecular function as yciC binds GTP as part of its metallochaperone mechanism. Supporting Evidence: PMID:34302342 the G3E family is thought to utilize GTP hydrolysis to thermodynamically drive and/or regulate metallocofactor assembly file:BACSU/yciC/yciC-falcon-research.md See deep research file for comprehensive analysis |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: Too general - more specific as GTPase activity for this zinc chaperone Reason: While yciC does hydrolyze GTP, GTPase activity is more specific and informative for the metallochaperone function. |
| GO:0140827 zinc chaperone activity | IDA PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallo... | NEW | Summary: Core molecular function - ZagA directly transfers zinc from CXCC motif to client proteins Reason: This represents the primary molecular function of yciC/ZagA as demonstrated by direct zinc transfer to FolE. Supporting Evidence: PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallochaperone and the alarmone ZTP under conditions of zinc deficiency. |
| GO:0003924 GTPase activity | IDA PMID:34302342 COG0523 proteins: a functionally diverse family of transitio... | NEW | Summary: Core enzymatic activity - GTP hydrolysis drives conformational changes for zinc transfer Reason: yciC requires GTP hydrolysis for its metallochaperone function, with zinc binding stimulating GTPase activity ~5-fold. Supporting Evidence: PMID:34302342 COG0523 proteins: a functionally diverse family of transition metal-regulated G3E P-loop GTP hydrolases from bacteria to man. |
| GO:0051604 protein maturation | IMP PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallo... | NEW | Summary: Core biological process - ZagA assists in metalloprotein maturation by zinc delivery Reason: ZagA directly transfers zinc to apo-FolE, enabling proper folding and function of this metalloenzyme. Supporting Evidence: PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallochaperone and the alarmone ZTP under conditions of zinc deficiency. |
| GO:0034224 cellular response to zinc ion starvation | IMP PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallo... | NEW | Summary: Key stress response process - ZagA is activated by ZTP alarmone during zinc limitation Reason: ZagA function is specifically activated by ZTP alarmone produced during zinc starvation conditions. Supporting Evidence: PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallochaperone and the alarmone ZTP under conditions of zinc deficiency. |
| GO:0009396 folic acid-containing compound biosynthetic process | IMP PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallo... | NEW | Summary: Critical metabolic process - ZagA supports folate biosynthesis via FolE metallation Reason: ZagA transfers zinc to FolE (GTP cyclohydrolase IA), which is essential for de novo folate biosynthesis. Supporting Evidence: PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallochaperone and the alarmone ZTP under conditions of zinc deficiency. |
| GO:0046654 tetrahydrofolate biosynthetic process | IMP PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallo... | NEW | Summary: Specific metabolic pathway - ZagA enables tetrahydrofolate production through FolE activation Reason: By providing zinc to FolE, ZagA directly supports the tetrahydrofolate biosynthetic pathway. Supporting Evidence: PMID:31132310 Bacillus subtilis FolE is sustained by the ZagA zinc metallochaperone and the alarmone ZTP under conditions of zinc deficiency. |
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Download this section (compressed HTML)Q: What determines the specificity of ZagA for different target metalloproteins beyond FolE?
Suggested experts: Metallobiochemistry researchers, Structural biologists, Bacterial physiology experts
Q: How does ZTP binding to ZagA induce conformational changes that enhance zinc transfer efficiency?
Suggested experts: Structural biologists, Biophysicists, Enzyme kinetics specialists
Q: What are the precise molecular mechanisms governing the ZMP→ZTP→ZagA feedback circuit?
Suggested experts: Systems biologists, Bacterial metabolism experts, Alarmone signaling researchers
Q: Are there other ZTP-responsive metallochaperones or is ZagA unique in this regulatory mechanism?
Suggested experts: Comparative genomics researchers, Metal homeostasis experts, Bacterial stress response specialists
Q: How is the timing of zinc transfer coordinated with target protein synthesis and folding?
Suggested experts: Protein folding researchers, Systems biologists, Bacterial genetics experts
Experiment: Systematic identification of all metalloprotein targets of ZagA beyond FolE to understand the full scope of its zinc chaperone function in B. subtilis metabolism.
Type: Substrate specificity analysis
Experiment: Detailed investigation of ZTP binding kinetics to ZagA, conformational changes upon ZTP binding, and quantitative analysis of how ZTP enhances zinc transfer efficiency to client proteins.
Type: ZTP alarmone mechanism analysis
Experiment: Detailed kinetic analysis of zinc transfer from ZagA to FolE and other targets, including the role of GTP hydrolysis and ZTP activation in the transfer mechanism.
Type: Zinc transfer kinetics
Experiment: Crystal structure of ZagA in zinc-bound and zinc-free states, with and without ZTP, and in complex with target proteins to understand the molecular mechanism of ZTP-activated zinc transfer.
Type: Structural studies
Experiment: Systematic analysis of the ZMP→ZTP→ZagA→FolE feedback circuit during zinc limitation, including temporal dynamics and quantitative relationships between metabolite levels.
Type: Feedback circuit analysis
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