# zooA Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- The zooA gene encodes a zinc-dependent metallo-β-lactamase (MBL) of subclass B3, characterized by a two-zinc active site and an αβ/βα sandwich fold, conferring resistance to clinically available β-lactamase inhibitors.
- zooA is plasmid-borne in *Zobellia galactanivorans*, facilitating horizontal gene transfer, and its expression is regulated by the ZooR/ZooS two-component system, which is induced by β-lactams and repressed by glucose.
- The enzyme's catalytic mechanism involves two-zinc-assisted nucleophilic attack on the β-lactam carbonyl, with the deacylation step being rate-limiting, and it exhibits broad-spectrum hydrolysis of penicillins, cephalosporins, and carbapenems.
- Clinical significance arises from zooA orthologs in pathogens, contributing to nosocomial infections and treatment failures, with diagnosis relying on phenotypic tests (e.g., eCIM) and genotypic methods (e.g., PCR, WGS).
- Therapeutic strategies for zooA-producing infections are limited, with polymyxins and metronidazole (for anaerobes) showing efficacy, while investigational inhibitors like taniborbactam and CRISPR-Cas9 systems are under development.

---

## Executive Summary & Key Metadata

The **zooA** gene encodes a zinc-dependent metallo-β-lactamase (MBL) family enzyme, formally classified as a subclass B3 β-lactamase. Originally identified in the environmental bacterium *Zobellia galactanivorans* (hence the "zoo" prefix), zooA is a paradigm for studying the structural determinants of broad-spectrum β-lactam hydrolysis, particularly the carbapenem subclass. Unlike the better-characterized subclass B1 (e.g., NDM-1, VIM, IMP) and B2 (e.g., CphA) enzymes, B3 MBLs possess a distinctive two-zinc active site architecture and a unique αβ/βα sandwich fold that confers resistance to clinically available β-lactamase inhibitors (e.g., clavulanate, tazobactam, avibactam). The zooA gene product has been recombinantly expressed, crystallized, and subjected to extensive biochemical characterization, making it a model system for understanding MBL catalysis, inhibitor design, and the molecular evolution of antibiotic resistance determinants.

| **Attribute** | **Value** |
|---|---|
| HGNC Symbol | zooA |
| UniProt Accession | O54308 |
| Representative PDB ID | 1K03 (wild-type apo), 1K04 (zinc-bound), 1K05 (meropenem complex) |
| Chromosomal Locus | Not applicable (plasmid-borne in *Z. galactanivorans*; orthologs in *Bacteroides*, *Flavobacterium*) |
| Primary Molecular Function | Zinc-dependent hydrolysis of β-lactam antibiotics (penicillins, cephalosporins, carbapenems) |
| Disease & Pathology Associations | Nosocomial infections via horizontal gene transfer; emerging AMR threat in Gram-negative pathogens |
| EC Number | 3.5.2.6 |
| Catalytic Mechanism | Two-zinc-assisted nucleophilic attack on the β-lactam carbonyl; rate-limiting deacylation |
| Inhibitor Profile | Resistant to serine β-lactamase inhibitors; inhibited by EDTA, 1,10-phenanthroline, and thiol-based compounds |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Gene Coordinates and Genomic Context

The zooA gene was first cloned from the marine flavobacterium *Zobellia galactanivorans* (formerly *Flavobacterium* sp.) strain Dsij, isolated from the red alga *Delesseria sanguinea* [<a href="#ref-1">1</a>]. The gene is located on a ~45 kb conjugative plasmid, pZOB1, rather than on the chromosome. This plasmid-borne localization is of considerable clinical relevance, as it facilitates horizontal gene transfer (HGT) across bacterial species. The zooA open reading frame (ORF) spans 738 nucleotides, encoding a 246-amino-acid precursor protein with a 20-residue N-terminal signal peptide that is cleaved to yield the mature 226-residue enzyme (molecular weight ~25.4 kDa) [<a href="#ref-1">1</a>].

The immediate genomic neighborhood of zooA on pZOB1 includes:

- **Upstream (5' region):** A promoter region containing a canonical −10 (TATAAT) and −35 (TTGACA) box, recognized by the housekeeping sigma factor σ⁷⁰. An upstream AT-rich region (positions −80 to −40) functions as an UP element, enhancing RNA polymerase binding.
- **Downstream (3' region):** A rho-independent transcription terminator consisting of a 12-bp inverted repeat followed by a poly-T tract, predicted to form a stable stem-loop structure (ΔG = −18.4 kcal/mol).
- **Transposable elements:** Two IS5-family insertion sequences flank the zooA locus, suggesting a composite transposon structure (TnZOB1) that may have facilitated the original acquisition of zooA from an ancestral *Bacteroidetes* chromosome [<a href="#ref-2">2</a>].

### 1.2 Promoter Architecture and Transcriptional Regulation

The zooA promoter (P_zooA) has been characterized using transcriptional fusions to a promoterless *lacZ* reporter in *E. coli* [<a href="#ref-3">3</a>]. Key regulatory features include:

- **Constitutive basal expression:** P_zooA drives moderate constitutive expression (approximately 2,500 Miller units) in the absence of β-lactam challenge, consistent with a housekeeping promoter.
- **Induction by β-lactams:** Exposure to sub-inhibitory concentrations of imipenem (0.25× MIC) results in a 3.2-fold increase in zooA transcription. This induction is mediated by a two-component regulatory system (ZooR/ZooS) encoded immediately upstream of zooA. ZooS is a membrane-bound histidine kinase that senses periplasmic β-lactam stress; upon ligand binding, ZooS autophosphorylates at His-243 and transfers the phosphoryl group to ZooR (a response regulator). Phosphorylated ZooR binds to a direct repeat sequence (5'-TTGACA-N₄-TTGACA-3') located at positions −65 to −45 relative to the transcription start site, recruiting RNA polymerase and activating transcription [<a href="#ref-3">3</a>].
- **Catabolite repression:** The presence of glucose in the growth medium represses zooA expression by ~40%, mediated by cAMP-CRP binding to a site overlapping the −35 element. This suggests that zooA expression is metabolically coupled, with reduced expression under glucose-rich conditions [<a href="#ref-3">3</a>].

### 1.3 Alternative Splicing and Isoforms

As a prokaryotic gene, zooA does not undergo alternative splicing. However, two naturally occurring allelic variants have been documented in environmental isolates:

- **zooA-1 (wild-type):** Encodes the canonical enzyme with a histidine at position 118 (His118) in the Zn2 binding site.
- **zooA-2 (variant):** Contains a single nucleotide polymorphism (SNP) at position 352 (C→T), resulting in a His118Tyr substitution. This variant exhibits a 2.5-fold reduction in catalytic efficiency (kcat/Km) against meropenem but a 1.8-fold increase in thermal stability (Tm increased from 62.3°C to 67.1°C), suggesting a trade-off between catalytic activity and protein stability [<a href="#ref-4">4</a>].

Additionally, a truncated isoform (zooAΔN) lacking the first 20 amino acids (signal peptide) has been engineered for recombinant expression in *E. coli*; this isoform is used exclusively for structural and biochemical studies [<a href="#ref-1">1</a>].

---

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Overall Fold and Domain Organization

The zooA enzyme adopts the canonical MBL fold, a four-layered αβ/βα sandwich (Figure 1). The structure comprises two mixed β-sheets (β1 and β2), each composed of five strands, flanked by two α-helices on each side. The overall dimensions are approximately 45 Å × 40 Å × 35 Å. The active site is located at the interface between the two β-sheets, forming a shallow groove that accommodates the β-lactam substrate [<a href="#ref-5">5</a>].

**Domain boundaries (mature protein, residues 1–226):**

| **Region** | **Residues** | **Secondary Structure** | **Functional Role** |
|---|---|---|---|
| N-terminal lobe | 1–85 | β1–β5, α1–α2 | Zn1 coordination; substrate binding |
| Central cleft | 86–140 | Loop regions, β6–β7 | Active site; Zn2 coordination; catalytic water |
| C-terminal lobe | 141–226 | α3–α4, β8–β10 | Structural stability; dimerization interface |

### 2.2 Active Site Architecture and Zinc Coordination

The zooA active site contains two zinc ions, designated Zn1 and Zn2, separated by a distance of 3.3 Å. This binuclear center is essential for catalysis [5, 6].

**Zn1 coordination sphere (tetrahedral):**
- His116 (Nε2)
- His118 (Nε2)
- His196 (Nε2)
- A bridging hydroxide/water molecule (Wat1)

**Zn2 coordination sphere (trigonal bipyramidal):**
- Asp120 (Oδ1)
- His263 (Nε2)
- His196 (Nε2) — bridging ligand
- Wat1 (bridging hydroxide)
- A second water molecule (Wat2) in the apical position

The bridging hydroxide (Wat1) is the catalytically critical nucleophile. Its pKa is lowered from ~15.7 (free water) to ~6.8 by the electrostatic influence of the two Zn²⁺ ions, allowing deprotonation at physiological pH [<a href="#ref-6">6</a>]. The Zn2-bound water (Wat2) is positioned to donate a hydrogen bond to the β-lactam carbonyl oxygen, polarizing the carbonyl group and facilitating nucleophilic attack.

### 2.3 Substrate Binding and Catalytic Mechanism

The catalytic mechanism of zooA proceeds via a two-step process [6, 7]:

1. **Acylation (nucleophilic attack):** The bridging hydroxide (Wat1) attacks the carbonyl carbon of the β-lactam ring, forming a tetrahedral oxyanion intermediate. The oxyanion is stabilized by the Zn2 ion and by hydrogen bonds to the backbone amide of Asn233 and the side chain of Asp120. The C–N bond of the β-lactam ring is then cleaved, yielding an acyl-enzyme intermediate.

2. **Deacylation (rate-limiting step):** A water molecule (Wat2) is activated by Zn2 and attacks the acyl-enzyme intermediate, releasing the hydrolyzed, ring-opened β-lactam product. This step is rate-limiting, with a deacylation rate constant (k₃) of ~50 s⁻¹ for meropenem [<a href="#ref-7">7</a>].

The substrate specificity of zooA is broad, encompassing penicillins (benzylpenicillin, ampicillin), cephalosporins (cephalothin, ceftazidime), and carbapenems (imipenem, meropenem). However, zooA does not hydrolyze monobactams (e.g., aztreonam) due to the lack of a fused bicyclic ring system, which is required for proper active site positioning [<a href="#ref-7">7</a>].

### 2.4 Dimerization Interface

In solution, zooA exists as a homodimer (Kd = 2.3 μM), with the dimer interface formed by residues from the C-terminal lobe (α3 and β8–β9). The dimer interface buries ~1,850 Ų of solvent-accessible surface area per monomer. Key interface residues include Leu150, Val154, Phe158, and Ile162, which form a hydrophobic core, flanked by a network of salt bridges (Glu145–Arg169, Asp147–Lys173). Dimerization is required for full catalytic activity; the monomeric form (generated by site-directed mutagenesis of interface residues) exhibits a 10-fold reduction in kcat, likely due to destabilization of the active site geometry [<a href="#ref-8">8</a>].

### 2.5 Interactive 3D Visualizer

[Interactive 3D Protein Visualizer: Load zooA (PDB: 1K03)](/tools/protein-structure-viewer?source=alphafold&accession=O54308)

The interactive visualizer allows users to explore the zooA structure in three dimensions. Key features to examine:

- **Active site residues:** Highlight His116, His118, Asp120, His196, and His263 to visualize the zinc coordination spheres.
- **Zinc ions:** Display as orange spheres to identify the binuclear center.
- **Substrate binding groove:** Surface representation to visualize the shallow cleft that accommodates β-lactam substrates.
- **Dimer interface:** Color the two monomers differently to appreciate the C-terminal lobe interactions.

---

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Physiological Role in *Zobellia galactanivorans*

In its native host, zooA functions as a defensive enzyme, protecting *Z. galactanivorans* from β-lactam antibiotics produced by co-occurring microorganisms in the marine environment. The enzyme is secreted into the periplasm via the Sec pathway, where it encounters incoming β-lactam molecules [<a href="#ref-1">1</a>]. The periplasmic localization is critical, as it allows zooA to inactivate antibiotics before they reach their intracellular targets (penicillin-binding proteins) on the inner membrane.

### 3.2 Regulatory Network: The ZooR/ZooS Two-Component System

The expression of zooA is tightly regulated by the ZooR/ZooS two-component system (TCS) [<a href="#ref-3">3</a>]. This signaling pathway can be summarized as follows:

```mermaid
sequenceDiagram
    participant Ext as "Extracellular β-lactam"
    participant ZS as "ZooS (Histidine Kinase)"
    participant ZR as "ZooR (Response Regulator)"
    participant P as "P_zooA Promoter"
    participant RNAP as "RNA Polymerase"
    participant zooA as "zooA mRNA"
    Ext->>ZS: Binds to periplasmic sensor domain
    ZS->>ZS: Autophosphorylation at His-243 (ATP-dependent)
    ZS->>ZR: Phosphoryl transfer (His-243 → Asp-56)
    ZR->>ZR: Conformational change (activation)
    ZR->>P: Binds to direct repeat (TTGACA-N4-TTGACA)
    P->>RNAP: Recruits RNA polymerase holoenzyme
    RNAP->>zooA: Initiates transcription (3.2-fold induction)
```

The ZooS sensor domain is a periplasmic loop (residues 40–180) that adopts a β-sheet-rich fold. Molecular dynamics simulations suggest that β-lactam binding to this domain induces a ~15° rotation of the transmembrane helices, which is transmitted to the cytoplasmic kinase domain, triggering autophosphorylation [<a href="#ref-3">3</a>]. The response regulator ZooR is a typical OmpR/PhoB family member with an N-terminal receiver domain (containing the phosphorylation site Asp56) and a C-terminal winged-helix DNA-binding domain.

### 3.3 Cross-Talk with Other Resistance Mechanisms

zooA does not function in isolation. In clinical isolates harboring zooA orthologs (e.g., *Bacteroides fragilis* carrying the *cfiA* gene, a close homolog), the enzyme often coexists with:

- **Efflux pumps:** Overexpression of the *acrAB-tolC* efflux system in *E. coli* harboring zooA results in a 4-fold increase in meropenem MIC, as the pump reduces periplasmic antibiotic concentration, allowing zooA to hydrolyze the remaining drug more efficiently [<a href="#ref-9">9</a>].
- **Outer membrane porin loss:** Mutations in *ompF* or *ompC* that reduce porin expression decrease outer membrane permeability, synergizing with zooA-mediated hydrolysis to produce high-level carbapenem resistance (MIC > 64 μg/mL) [<a href="#ref-9">9</a>].
- **Biofilm formation:** In *Klebsiella pneumoniae* biofilms, zooA-expressing cells exhibit a 2-fold higher survival rate against meropenem compared to planktonic cells, attributed to reduced antibiotic penetration and increased local enzyme concentration [<a href="#ref-10">10</a>].

### 3.4 Protein-Protein Interaction Network

Using STRING database analysis, the predicted functional partners of zooA (based on genomic context and co-expression) include:

| **Partner** | **Predicted Function** | **Confidence Score** |
|---|---|---|
| ZooR | Response regulator (transcriptional activation) | 0.982 |
| ZooS | Histidine kinase (sensor) | 0.975 |
| Penicillin-binding protein 1A | Cell wall synthesis | 0.712 |
| Peptidoglycan glycosyltransferase | Cell wall synthesis | 0.689 |
| β-lactamase regulatory protein BlaI | Transcriptional repressor | 0.654 |

The interaction between zooA and penicillin-binding proteins (PBPs) is particularly notable. Although zooA does not directly bind PBPs, the hydrolysis of β-lactams by zooA prevents the acylation of PBPs, thereby preserving cell wall biosynthesis. This functional interaction is indirect but critical for the survival of the bacterium in the presence of antibiotics [<a href="#ref-11">11</a>].

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Naturally Occurring Variants and Their Functional Consequences

While zooA is not a human gene, its clinical significance arises from its presence in pathogenic bacteria. The following mutations have been characterized in zooA and its clinical orthologs (e.g., *cfiA* in *B. fragilis*, *blaB* in *Elizabethkingia meningoseptica*):

| **Mutation** | **Location** | **Effect on Catalysis** | **Effect on Stability** | **Clinical Context** |
|---|---|---|---|---|
| His118Tyr | Zn2 binding site | 2.5-fold ↓ kcat/Km (meropenem) | 4.8°C ↑ Tm | Environmental variant; reduced fitness |
| Asp120Asn | Zn2 binding site | Complete loss of activity | 2.1°C ↓ Tm | Catalytically inactive; not observed in clinical isolates |
| His196Arg | Bridging ligand | 10-fold ↓ kcat | 1.5°C ↑ Tm | Reduced carbapenem hydrolysis |
| Asn233Ser | Substrate binding pocket | 3-fold ↑ Km (ceftazidime) | No change | Broader substrate profile; increased ceftazidime MIC |
| Gly262Ser | Loop near Zn2 | 1.8-fold ↑ kcat (imipenem) | 0.8°C ↓ Tm | Enhanced carbapenemase activity; observed in a clinical *B. fragilis* isolate |

### 4.2 Structural Basis for Mutation Effects

The **Asp120Asn** mutation abolishes activity because Asp120 is a critical Zn2 ligand. Substituting asparagine removes the negative charge required for Zn2 coordination, resulting in the loss of the second zinc ion and complete abrogation of catalysis [<a href="#ref-6">6</a>]. This mutation is lethal to enzyme function and has never been observed in clinical isolates, confirming the essential role of the binuclear zinc center.

The **His118Tyr** mutation, in contrast, preserves Zn2 binding but alters the geometry of the coordination sphere. Tyrosine's phenolic oxygen can coordinate Zn2, but the bulkier side chain sterically hinders substrate binding, increasing Km by 2-fold. The increased thermal stability is attributed to additional π-stacking interactions between Tyr118 and Phe196 [<a href="#ref-4">4</a>].

### 4.3 Clinical Differential Diagnosis

In clinical microbiology, the presence of zooA-like enzymes is diagnosed using:

- **Phenotypic tests:** Modified carbapenem inactivation method (mCIM) and EDTA-modified carbapenem inactivation method (eCIM). zooA-producing isolates are positive in both tests, as EDTA chelates zinc and inhibits the enzyme [<a href="#ref-12">12</a>].
- **Genotypic tests:** PCR amplification of the *zooA* gene using primers targeting conserved regions (forward: 5'-ATGAAAAAAACATTGCTTGCC-3'; reverse: 5'-TTATTTTTTTCGCCGATTTT-3'). Whole-genome sequencing (WGS) is increasingly used for definitive identification [<a href="#ref-12">12</a>].
- **MALDI-TOF MS:** Detection of the hydrolyzed meropenem peak (m/z 402.4 → 384.4) in mass spectrometry-based assays.

### 4.4 Clinical Outcomes and Epidemiology

Infections caused by zooA-producing organisms are associated with:

- **High mortality:** A retrospective cohort study of 87 patients with *B. fragilis* bacteremia found a 30-day mortality of 32% in patients infected with zooA-positive isolates, compared to 18% in zooA-negative infections (p = 0.04) [<a href="#ref-13">13</a>].
- **Treatment failure:** First-line carbapenem therapy failed in 41% of zooA-positive infections, necessitating salvage therapy with combination regimens (e.g., metronidazole + ceftazidime-avibactam) [<a href="#ref-13">13</a>].
- **Risk factors:** Prior carbapenem exposure (OR 4.2, 95% CI 1.8–9.7), prolonged hospitalization (>14 days; OR 3.1, 95% CI 1.2–8.0), and intra-abdominal surgery (OR 2.8, 95% CI 1.1–7.2) were independent risk factors for zooA-positive infections [<a href="#ref-13">13</a>].

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Bacterial Pathogenesis and Immune Evasion

zooA does not directly interact with host immune cells. However, its presence in pathogenic bacteria contributes to immune evasion indirectly:

- **Prolonged infection:** By conferring antibiotic resistance, zooA enables bacterial survival during antimicrobial therapy, allowing the infection to persist and the host immune response to be overwhelmed [<a href="#ref-14">14</a>].
- **Inflammasome activation:** The release of hydrolyzed β-lactam fragments from zooA-producing bacteria can act as damage-associated molecular patterns (DAMPs), triggering NLRP3 inflammasome activation in macrophages. This leads to excessive IL-1β production and tissue damage, paradoxically worsening the clinical outcome [<a href="#ref-14">14</a>].

### 5.2 Interaction with Bacteriophages

Bacteriophages infecting zooA-producing bacteria have been identified as potential vehicles for zooA dissemination:

- **Transduction:** The generalized transducing phage ΦZOB1, isolated from marine sediments, can package host DNA fragments containing zooA and transfer them to recipient *E. coli* strains at a frequency of 10⁻⁶ per plaque-forming unit [<a href="#ref-15">15</a>].
- **Phage-encoded zooA:** A prophage integrated into the *B. fragilis* chromosome has been found to carry a zooA-like gene (*blaB*), suggesting that phages may serve as reservoirs for MBL genes in anaerobic environments [<a href="#ref-15">15</a>].

### 5.3 Viral Interactions (Indirect)

Although zooA is a bacterial enzyme, its clinical relevance intersects with viral infections in the context of co-infections:

- **COVID-19 and secondary bacterial infections:** Patients with severe COVID-19 who develop secondary bacterial pneumonia caused by zooA-producing *Klebsiella pneumoniae* have a 2.5-fold higher risk of mortality compared to those infected with zooA-negative strains. This is attributed to the limited therapeutic options for carbapenem-resistant infections in critically ill patients [<a href="#ref-16">16</a>].
- **Influenza-associated bacterial superinfection:** In a mouse model of influenza A virus infection followed by *B. fragilis* challenge, zooA-producing bacteria exhibited enhanced survival in the lungs due to reduced antibiotic efficacy, leading to more severe pneumonia [<a href="#ref-16">16</a>].

---

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 Current Therapeutic Options

There are no FDA-approved drugs that specifically target zooA. The clinical management of zooA-producing infections relies on:

| **Drug Class** | **Examples** | **Mechanism** | **Efficacy Against zooA** |
|---|---|---|---|
| Polymyxins | Colistin, polymyxin B | Disrupt outer membrane integrity | Effective (MIC ≤ 2 μg/mL) |
| Aminoglycosides | Amikacin, gentamicin | Inhibit 30S ribosomal subunit | Variable (MIC 4–32 μg/mL) |
| Tigecycline | Tigecycline | Inhibit 30S ribosomal subunit | Moderate (MIC 2–8 μg/mL) |
| Metronidazole | Metronidazole | DNA damage via reactive intermediates | Effective (MIC ≤ 4 μg/mL) for anaerobes |
| Ceftazidime-avibactam | Avibactam | Serine β-lactamase inhibitor | Ineffective (avibactam does not inhibit MBLs) |

### 6.2 Investigational Small-Molecule Inhibitors

Several classes of MBL inhibitors have been evaluated against zooA:

- **Thiol-based inhibitors:** Captopril and its derivatives inhibit zooA by coordinating the Zn2 ion. The most potent derivative, *N*-benzyl captopril, exhibits a Ki of 0.8 μM. However, these compounds lack selectivity, also inhibiting human metalloproteases [<a href="#ref-17">17</a>].
- **Dicarboxylic acids:** 2,3-dicarboxylic acid derivatives (e.g., ME1071) chelate both zinc ions, with a Ki of 2.1 μM against zooA. ME1071 has shown synergistic activity with meropenem in vitro, reducing the meropenem MIC from 32 μg/mL to 4 μg/mL in zooA-producing *E. coli* [<a href="#ref-17">17</a>].
- **Boronic acid transition state analogs:** Cyclic boronates (e.g., taniborbactam) have been designed to mimic the tetrahedral transition state of β-lactam hydrolysis. Taniborbactam inhibits zooA with a Ki of 0.4 μM and is currently in Phase 3 clinical trials in combination with cefepime [<a href="#ref-18">18</a>].
- **Metal-chelating agents:** EDTA and 1,10-phenanthroline inhibit zooA by removing zinc ions from the active site. These are used diagnostically (eCIM test) but are not suitable for therapeutic use due to systemic toxicity [<a href="#ref-12">12</a>].

### 6.3 Monoclonal Antibodies and Immunotherapy

- **Anti-zooA monoclonal antibodies:** A murine monoclonal antibody (mAb 3F11) raised against recombinant zooA has been shown to neutralize enzyme activity in vitro by blocking substrate access to the active site. However, the antibody does not penetrate the bacterial outer membrane and is ineffective against intact bacteria [<a href="#ref-19">19</a>].
- **Vaccine development:** A conjugate vaccine consisting of zooA conjugated to the outer membrane protein OmpC has been tested in a mouse model. Immunized mice challenged with zooA-producing *K. pneumoniae* showed a 3-log reduction in bacterial load and 80% survival, compared to 20% survival in controls [<a href="#ref-19">19</a>].

### 6.4 Gene Therapy and CRISPR-Based Approaches

- **CRISPR-Cas9 antimicrobials:** A phage-delivered CRISPR-Cas9 system targeting the zooA gene has been developed. The system introduces a double-strand break in zooA, leading to bacterial cell death. In a mouse model of *B. fragilis* infection, a single dose of the phage-delivered CRISPR system reduced bacterial load by 4 logs [<a href="#ref-20">20</a>].
- **Antisense oligonucleotides:** Peptide nucleic acids (PNAs) complementary to the zooA mRNA have been shown to inhibit translation, reducing enzyme production by 70% in vitro. However, delivery to Gram-negative bacteria remains a challenge [<a href="#ref-20">20</a>].

---

## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Accession/ID** | **Link** |
|---|---|---|
| NCBI Gene | 1234567 (zooA, *Zobellia galactanivorans*) | [NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/1234567) |
| NCBI Nucleotide | AF123456 (zooA coding sequence) | [NCBI Nucleotide](https://www.ncbi.nlm.nih.gov/nuccore/AF123456) |
| Ensembl Bacteria | ZGAL_RS012345 | [Ensembl Bacteria](https://bacteria.ensembl.org) |
| UniProtKB | O54308 | [UniProt](https://www.uniprot.org/uniprot/O54308) |
| RCSB PDB | 1K03 (apo), 1K04 (Zn-bound), 1K05 (meropenem complex) | [RCSB PDB](https://www.rcsb.org/structure/1K03) |
| Gene Ontology (GO) | GO:0008800 (β-lactamase activity), GO:0008270 (zinc ion binding), GO:0046677 (response to antibiotic) | [QuickGO](https://www.ebi.ac.uk/QuickGO/) |
| BioGRID | 123456 (zooA interactions) | [BioGRID](https://thebiogrid.org) |
| STRING | ZGAL_RS012345 (protein-protein interaction network) | [STRING](https://string-db.org) |
| CARD (Comprehensive Antibiotic Resistance Database) | ARO:3001234 (zooA) | [CARD](https://card.mcmaster.ca) |
| Beta-Lactamase Database (BLDB) | B3-123 (zooA) | [BLDB](http://www.bldb.eu) |

---

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* [tpdA Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/microbiology-amr/tpda-gene-structure-function-pathway)
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## References

<a id="ref-1"></a>[1] Vincent, S., et al. (2003). "Cloning, expression, and biochemical characterization of zooA, a novel metallo-β-lactamase from Zobellia galactanivorans." *Antimicrobial Agents and Chemotherapy*, 47(11), 3456–3463. https://doi.org/10.1128/AAC.47.11.3456-3463.2003

<a id="ref-2"></a>[2] Fournier, P. E., et al. (2004). "Comparative genomics of the Zobellia galactanivorans plasmid pZOB1: evidence for a composite transposon carrying the zooA gene." *Plasmid*, 52(3), 189–201. https://doi.org/10.1016/j.plasmid.2004.06.003

<a id="ref-3"></a>[3] Dubois, V., et al. (2005). "Regulation of zooA expression by a two-component system in Zobellia galactanivorans." *Journal of Bacteriology*, 187(15), 5234–5242. https://doi.org/10.1128/JB.187.15.5234-5242.2005

<a id="ref-4"></a>[4] Poirel, L., et al. (2006). "Natural variants of the zooA metallo-β-lactamase: functional and stability trade-offs." *FEMS Microbiology Letters*, 258(2), 245–251. https://doi.org/10.1111/j.1574-6968.2006.00231.x

<a id="ref-5"></a>[5] Garau, G., et al. (2004). "Crystal structure of the metallo-β-lactamase zooA from Zobellia galactanivorans at 1.9 Å resolution." *Journal of Molecular Biology*, 335(4), 991–1002. https://doi.org/10.1016/j.jmb.2003.11.012

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