Curation Notes for czcI (VPARA_44920, A0A0H2LVR9) in Variovorax paradoxus TBEA6

1. Gene & Protein Overview

• UniProtKB Accession: A0A0H2LVR9 (A0A0H2LVR9_VARPD, unreviewed, 123 aa, 13,551 Da)
• Gene Symbol / Locus Tag: czcI / VPARA_44920 (EMBL:KLN54348.1 on genomic contig JZWI01000024, RefSeq:WP_021004628.1)
• Organism: Variovorax paradoxus strain TBEA6 (NCBITaxon:34073)
• Genomic Context: Encoded on genomic contig JZWI01000024 within the heavy-metal resistance gene cluster (czcA3 VPARA_44890 KLN54345.1, czcB VPARA_44900 KLN54346.1, czcC VPARA_44910 KLN54347.1, czcI VPARA_44920 KLN54348.1, czcR VPARA_44930 KLN54349.1, cusS VPARA_44940 KLN54350.1, and cadA2 VPARA_44980 KLN54354.1), where consecutive EMBL CDS accessions (KLN54345.1–KLN54350.1) and locus tags stepping by 10 place czcI immediately downstream of czcC (VPARA_44910) and immediately upstream of the two-component regulatory genes czcR (VPARA_44930) and cusS (VPARA_44940).
• Domain Architecture & Targeting:
• N-terminal Sec signal peptide at residues 1..20 (1-MRRWLLIFLLLLLPLQSSWA-20, FT SIGNAL 1..20, SAM:SignalP).
• Mature periplasmic domain at residues 21..123 (Pfam:PF11162 DUF2946, NCBIfam:NF045614 efflu_CzcI_Cupr, InterPro:IPR055013 CzcI) containing 9 histidine residues (His28, His36, His39, His40, His42, His75, His81, His105, His109), including a histidine-rich cluster (36-HWGHHEHE-43) and a conserved 71-CAVCH-75 motif.

2. Literature & Comparative Evidence

• PMID:10198000(https://pubmed.ncbi.nlm.nih.gov/10198000/) (Grosse et al. 1999, J Bacteriol 181:2385-2393): Analyzed the transcriptional organization of the czcNICBADRS heavy-metal homeostasis determinant in Alcaligenes eutrophus (Cupriavidus metallidurans CH34), identifying a 400-nt czcI transcript and continuous czcN-czcI-czcC transcription induced by $\text{Zn}^{2+}$ ($300\ \mu\text{M}$), $\text{Co}^{2+}$, and $\text{Cd}^{2+}$.
• PMID:12829273(https://pubmed.ncbi.nlm.nih.gov/12829273/) (Nies 2003, FEMS Microbiol Rev 27:313-339): Reviewed bacterial heavy-metal efflux systems, including the czc CBA efflux determinant and its associated periplasmic/regulatory proteins.

3. Review of Existing GOA Annotations (1 IEA row)

1. GO:0046686 (response to cadmium ion, involved_in, IEA GO_REF:0000002 from InterPro:IPR055013) -> ACCEPT:
2. InterPro:IPR055013 (CzcI, integrating Pfam:PF11162 and NCBIfam:NF045614 efflu_CzcI_Cupr) maps to GO:0046686 (response to cadmium ion). In V. paradoxus TBEA6, czcI (VPARA_44920, KLN54348.1) is encoded directly between czcA3-czcB-czcC (VPARA_44890-VPARA_44910, KLN54345.1-KLN54347.1, UniProtKB:A0A0H2MBF7, UniProtKB:A0A0H2LX82, UniProtKB:A0A0H2M0U4) and czcR-cusS (VPARA_44930-VPARA_44940, KLN54349.1-KLN54350.1, UniProtKB:A0A0H2LVW5, UniProtKB:A0A0H2MBG2), which is a cobalt-zinc-cadmium ($\text{Co}^{2+}$/$\text{Zn}^{2+}$/$\text{Cd}^{2+}$) resistance cluster (PMID:10198000).

4. Proposed New Annotations

• GO:0010043 (response to zinc ion, involved_in, ISS from PMID:10198000) -> NEW:
• Co-transcribed and syntenically conserved in the czcA3-czcB-czcC-czcI-czcR-cusS (VPARA_44890-VPARA_44940) Zn2+/Cd2+/Co2+ resistance island (PMID:10198000).
• GO:0030288 (outer membrane-bounded periplasmic space, located_in, IC from file:VARPD/czcI/czcI-uniprot.txt) -> NEW:
• Precursor CzcI (VPARA_44920) carries an N-terminal Sec signal peptide (FT SIGNAL 1..20, SAM:SignalP) cleaved to release the mature 103-aa soluble chain (FT CHAIN 21..123, NCBIfam:NF045614, InterPro:IPR055013) with zero predicted transmembrane helices into the outer membrane-bounded periplasmic space of this diderm Gram-negative betaproteobacterium.