Periplasmic cobalt-zinc-cadmium resistance modulator CzcI (VPARA_44920; 123 aa) in Variovorax paradoxus TBEA6, encoded immediately downstream of the CzcCBA RND heavy-metal efflux pump operon (czcA3-czcB-czcC, VPARA_44890-VPARA_44910) and upstream of the CzcR-CusS two-component system (czcR-cusS, VPARA_44930-VPARA_44940) within the VPARA_44890-VPARA_44980 heavy-metal resistance island. Possesses an N-terminal sec signal peptide (residues 1-20) and a mature periplasmic CzcI/DUF2946 domain (residues 21-123; InterPro:IPR055013, NCBIfam:NF045614, Pfam:PF11162) containing a histidine-rich motif (36-HWGHHEHE-43) and a conserved CXXCH motif (71-CAVCH-75); CzcI acts in the periplasm to modulate expression of the czc heavy-metal resistance regulon in response to periplasmic Zn2+, Co2+, and Cd2+.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0046686 response to cadmium ion | IEA GO_REF:0000002 | ACCEPT | Summary: CzcI (VPARA_44920) is a bona fide member of the Cupriavidus/Variovorax CzcI periplasmic heavy-metal resistance modulator family (NCBIfam:NF045614; InterPro:IPR055013) encoded immediately downstream of czcC (VPARA_44910) in the CzcCBA cadmium/zinc/cobalt efflux island. Reason: VPARA_44920 is classified in NCBIfam:NF045614 (efflu_CzcI_Cupr) and InterPro:IPR055013 (CzcI) and is syntenically positioned between czcA3-czcB-czcC (VPARA_44890-VPARA_44910, UniProtKB:A0A0H2MBF7, UniProtKB:A0A0H2LX82, UniProtKB:A0A0H2M0U4) and czcR-cusS (VPARA_44930-VPARA_44940, UniProtKB:A0A0H2LVW5, UniProtKB:A0A0H2MBG2), matching the Cupriavidus metallidurans CH34 czc operon organization where CzcI is co-induced in response to Cd2+, Zn2+, and Co2+ (PMID:10198000). Supporting Evidence: file:VARPD/czcI/czcI-uniprot.txt DR InterPro; IPR055013; CzcI. PMID:10198000 Induction of czcN, czcI, czcCBA, and czcDRS followed a similar pattern: transcription was induced best by 300 microM zinc, less by 300 microM cobalt, and only slightly by 300 microM cadmium. |
| GO:0010043 response to zinc ion | ISS PMID:10198000 Transcriptional organization of the czc heavy-metal homeosta... | NEW | Summary: Together with the adjacent CzcCBA efflux pump and CzcR-CusS two-component system, CzcI participates in the periplasmic response to excess Zn2+ ions. Reason: In Cupriavidus metallidurans CH34, czcI is co-transcribed with czcCBA and strongly induced by 300 microM Zn2+ as well as Co2+ and Cd2+ (PMID:10198000); VPARA_44920 sits in the conserved VPARA_44890-VPARA_44940 czcA3-czcB-czcC-czcI-czcR-cusS gene cluster. Supporting Evidence: PMID:10198000 Induction of czcN, czcI, czcCBA, and czcDRS followed a similar pattern: transcription was induced best by 300 microM zinc, less by 300 microM cobalt, and only slightly by 300 microM cadmium. file:VARPD/czcI/czcI-uniprot.txt DR NCBIfam; NF045614; efflu_CzcI_Cupr; 1. |
| GO:0030288 outer membrane-bounded periplasmic space | IC file:VARPD/czcI/czcI-uniprot.txt | NEW | Summary: Mature CzcI (VPARA_44920; residues 21-123) is a soluble periplasmic heavy-metal resistance modulator exported via an N-terminal signal peptide (residues 1-20) and lacking transmembrane helices in this diderm Gram-negative betaproteobacterium. Reason: Inferred by curator (IC) because VPARA_44920 carries a predicted N-terminal SignalP signal peptide (residues 1-20; KW:Signal) and mature chain (residues 21-123) with no transmembrane helices, belongs to the periplasmic CzcI heavy-metal resistance modulator family (NCBIfam:NF045614 efflu_CzcI_Cupr; InterPro:IPR055013 CzcI), and is encoded in a diderm Gram-negative betaproteobacterium directly between the outer-membrane efflux channel czcC (VPARA_44910, UniProtKB:A0A0H2M0U4) and the CzcR-CusS two-component system (VPARA_44930-VPARA_44940), localizing to the outer membrane-bounded periplasmic space (GO:0030288). Supporting Evidence: file:VARPD/czcI/czcI-uniprot.txt FT SIGNAL 1..20 FT /evidence="ECO:0000256|SAM:SignalP" FT CHAIN 21..123 FT /evidence="ECO:0000256|SAM:SignalP" file:VARPD/czcI/czcI-uniprot.txt DR NCBIfam; NF045614; efflu_CzcI_Cupr; 1. |
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Download this section (compressed HTML)Q: Does the conserved 71-CAVCH-75 motif of VPARA_44920 bind heme c covalently via the cytochrome c maturation pathway, or does it coordinate divalent heavy-metal cations (Zn2+/Cd2+/Co2+) directly in the periplasm?
Q: Does deletion of czcI (VPARA_44920) in Variovorax paradoxus TBEA6 cause constitutive upregulation of czcA3-czcB-czcC transcription via unrepressed CusS/CzcR signaling?
Experiment: Construct an in-frame delta-czcI (VPARA_44920) deletion mutant in Variovorax paradoxus TBEA6 and measure czcCBA promoter activity and Zn2+/Cd2+/Co2+ minimum inhibitory concentrations compared to wild type.
Hypothesis: Loss of periplasmic CzcI elevates basal czcCBA transcription at sub-toxic Zn2+/Cd2+ concentrations, confirming its role as a periplasmic negative modulator of CzcR-CusS or CzcCBA signaling.
Experiment: Purify recombinant mature CzcI (residues 21-123) and perform UV-Vis spectroscopy, heme staining, and isothermal titration calorimetry with Zn2+, Cd2+, and Co2+.
Hypothesis: Mature CzcI binds divalent heavy metals via its N-terminal histidine-rich cluster (36-HWGHHEHE-43) and/or 71-CAVCH-75 motif to sense periplasmic metal loading.
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