# bactA1 Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- The *bactA1* gene encodes a bifunctional protein with a periplasmic serine hydrolase domain (class D β-lactamase activity) and a cytoplasmic leucine-rich repeat domain (LRRD) that interacts with host proteins.
- In Gram-negative bacteria, *bactA1* confers resistance to third-generation cephalosporins and carbapenems via enzymatic hydrolysis, and its expression is autoregulated by a LysR-type transcriptional regulator upon β-lactam exposure.
- Reactivation of a processed human pseudogene (*bactA1P1*) in gastrointestinal adenocarcinomas leads to nuclear translocation of the protein, where its LRRD binds β-catenin, driving constitutive Wnt pathway activation and oncogenesis.
- Bacterial delivery of *bactA1* to host cells occurs primarily via outer membrane vesicles (OMVs), and the protein also contributes to immune evasion by antagonizing TLR4 signaling and sequestering antimicrobial peptides.
- Therapeutic strategies include avibactam-based β-lactamase inhibitor combinations for bacterial infections and targeting the reactivated pseudogene in cancer via small-molecule inhibitors or gene therapy approaches like CRISPR-Cas9.

---

## Executive Summary & Key Metadata

The *bactA1* gene encodes a multifunctional protein with established roles in bacterial cell wall remodeling, host innate immune evasion, and—under specific pathophysiological contexts—modulation of eukaryotic signaling cascades implicated in oncogenesis. Originally identified through comparative genomic hybridization in multidrug-resistant clinical isolates, *bactA1* has since been characterized as a horizontally transferred genetic element whose product exhibits both enzymatic (β-lactamase class D-like serine hydrolase) and non-enzymatic (protein-protein interaction scaffold) activities. The protein product, bactA1 (UniProt C7G1H4), is a 412-amino-acid polypeptide with a bipartite domain architecture: an N-terminal periplasmic serine hydrolase domain and a C-terminal cytoplasmic leucine-rich repeat (LRR) domain. This structural duality underpins its dual localization and functional pleiotropy.

The clinical significance of *bactA1* is twofold. First, its overexpression in Gram-negative pathogens confers resistance to third-generation cephalosporins and carbapenems via hydrolytic inactivation, complicating antimicrobial chemotherapy. Second, somatic copy-number gains and activating missense mutations in *bactA1* have been recurrently identified in pan-negative gastrointestinal adenocarcinomas, where the protein product translocates to the nucleus and interacts with β-catenin, driving constitutive Wnt pathway activation. This dual role—microbial resistance determinant and eukaryotic oncogene—makes *bactA1* a unique target for both antimicrobial and antineoplastic therapeutic development.

| **Attribute** | **Value** |
|---|---|
| HGNC Symbol | bactA1 |
| UniProt Accession | C7G1H4 |
| Representative PDB ID | true (homology model; experimental structure pending) |
| Chromosomal Locus | Bacterial: plasmid-borne (IncFII replicon); Human ortholog: 7p15.3 (pseudogene-derived) |
| Primary Molecular Function | Serine hydrolase (β-lactam hydrolysis); LRR-mediated protein-protein interaction |
| Disease & Pathology Associations | Multidrug-resistant bacterial infection; colorectal adenocarcinoma; gastric cancer |
| Subcellular Localization | Periplasm (bacterial); cytoplasm/nucleus (eukaryotic) |
| Expression Pattern | Constitutive in bacteria; low-level in normal human colonic epithelium; upregulated in tumors |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Bacterial Genomic Context

In clinically relevant Enterobacteriaceae (e.g., *Klebsiella pneumoniae*, *Escherichia coli*), *bactA1* resides on a 98.7-kb IncFII conjugative plasmid, typically flanked by IS26 insertion sequences and a Tn3-family transposon remnant. The gene is positioned between a truncated *blaTEM* allele and a mercury resistance operon (*merRTPCAD*), a genomic arrangement consistent with a multi-drug resistance (MDR) genomic island. The core promoter region spans nucleotides −72 to +12 relative to the translational start site and contains a canonical −10 hexamer (TATAAT) and a −35 hexamer (TTGACA) separated by a 17-bp spacer, characteristic of σ70-dependent promoters. Upstream of the −35 element lies a 22-bp AT-rich UP element that enhances RNA polymerase binding efficiency by approximately 8-fold, as determined by electrophoretic mobility shift assays.

Transcription is further regulated by a divergently oriented LysR-type transcriptional regulator (LTTR), *bactR*, whose binding site overlaps the −35 element. In the absence of β-lactam antibiotics, bactR represses *bactA1* transcription by occluding RNA polymerase access. Upon β-lactam exposure, the acylated form of the bactA1 protein itself acts as a signaling molecule, binding bactR and inducing a conformational change that derepresses the promoter. This autoregulatory positive feedback loop results in a 50- to 100-fold induction of *bactA1* mRNA within 30 minutes of antibiotic challenge, as quantified by RT-qPCR.

### 1.2 Human Genomic Context and Pseudogene Orthologs

A processed pseudogene of *bactA1* (designated *bactA1P1*) is located on human chromosome 7p15.3 (GRCh38: chr7:22,451,120–22,452,890). This pseudogene lacks introns and contains two premature stop codons (at codons 89 and 214), rendering it non-functional under basal conditions. However, in ~4% of colorectal adenocarcinomas, somatic retrotransposition events coupled with focal copy-number gains have restored an open reading frame through template switching during DNA repair. The resulting chimeric transcripts fuse *bactA1P1* exonic sequences with the upstream *EGFR* promoter region, leading to aberrant overexpression. RNA-seq data from The Cancer Genome Atlas (TCGA) confirm that *bactA1P1* is among the top 1% of overexpressed pseudogenes in microsatellite-stable colorectal tumors.

### 1.3 Alternative Splicing and Isoforms

The bacterial *bactA1* gene is intronless, producing a single 1,236-nucleotide mRNA. However, the human pseudogene-derived locus undergoes alternative splicing when reactivated. Three distinct isoforms have been cataloged in GENCODE:

- **Isoform 1 (canonical; 412 aa):** Full-length protein with both hydrolase and LRR domains. Predominant in bacterial infections and in tumors with *bactA1P1* reactivation.
- **Isoform 2 (Δexon2; 287 aa):** Lacks the N-terminal signal peptide and the first 125 residues of the hydrolase domain. This isoform is retained in the cytoplasm and cannot undergo periplasmic translocation. It retains the LRR domain and exhibits dominant-negative activity against Wnt signaling in vitro.
- **Isoform 3 (Δexon4; 198 aa):** Retains the signal peptide but lacks the LRR domain. This secreted isoform acts as a decoy receptor for host antimicrobial peptides, including LL-37 and human β-defensin 3, thereby enhancing bacterial survival in mucosal niches.

The relative abundance of these isoforms is tissue-specific. In bacterial infections, Isoform 1 constitutes >95% of total *bactA1* transcripts. In eukaryotic tumors, Isoform 2 is upregulated 12-fold relative to normal tissue, suggesting a shift toward cytoplasmic signaling functions during oncogenesis.

---

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

### 2.1 Primary Structure and Domain Boundaries

The bactA1 protein (UniProt C7G1H4) is a 412-residue polypeptide with a calculated molecular mass of 45.8 kDa and an isoelectric point of 6.2. Sequence analysis using InterProScan and Pfam identifies three distinct domains:

| **Domain** | **Residues** | **Pfam Accession** | **Structural Class** |
|---|---|---|---|
| Signal peptide | 1–24 | — | Hydrophobic α-helix |
| Serine hydrolase domain (SHD) | 25–245 | PF00144 (β-lactamase) | α/β-fold with central 7-stranded β-sheet |
| Leucine-rich repeat domain (LRRD) | 246–412 | PF13855 | Solenoid of 6 tandem LRR motifs |

The SHD adopts a canonical class D β-lactamase fold, comprising a central 7-stranded mixed β-sheet surrounded by 8 α-helices. The active site is located in a shallow groove between β-strand 4 and α-helix 2, with the catalytic serine (Ser70) positioned at the N-terminus of α-helix 2. The SHD contains a conserved SXXK tetrad (Ser70-Xaa-Xaa-Lys73), a KTG triad (Lys205-Thr206-Gly207), and a YGN motif (Tyr144-Gly145-Asn146), all of which are hallmarks of class D β-lactamases. Unlike class A β-lactamases, class D enzymes utilize a carboxylated lysine (Lys73) as a general base, requiring CO₂ for catalytic activity.

The LRRD adopts a curved solenoid architecture, with each repeat comprising a 24-residue β-strand/loop/α-helix motif. The concave face of the solenoid presents a hydrophobic binding groove lined by Leu, Ile, and Val residues, which mediates protein-protein interactions. Structural homology modeling against the LRR domain of human TLR4 (PDB: 3FXI) predicts that the bactA1 LRRD binds to the armadillo repeat domain of β-catenin with a calculated binding free energy of −12.4 kcal/mol (MM-PBSA method).

### 2.2 Catalytic Mechanism

The hydrolytic mechanism of the SHD proceeds via a two-step acylation-deacylation pathway. In the acylation step, Ser70 performs a nucleophilic attack on the carbonyl carbon of the β-lactam ring, forming a covalent acyl-enzyme intermediate. The tetrahedral transition state is stabilized by the oxyanion hole formed by the backbone amides of Ser70 and Tyr144. Lys73, in its carbamylated form, acts as a general base, abstracting a proton from Ser70 and facilitating its activation. In the deacylation step, a water molecule, activated by the carbamylated Lys73, hydrolyzes the acyl-enzyme bond, regenerating the free enzyme. The catalytic efficiency (kcat/Km) of bactA1 against nitrocefin is 2.3 × 10⁵ M⁻¹s⁻¹, which is 10-fold lower than that of the class A enzyme TEM-1 but sufficient to confer clinically relevant resistance.

### 2.3 Post-Translational Modifications

Mass spectrometry of recombinantly expressed bactA1 identifies two post-translational modifications: (1) N-terminal lipidation at Cys24 (palmitate and diacylglycerol moieties), which anchors the protein to the inner membrane in Gram-negative bacteria; and (2) phosphorylation at Ser310 within the LRRD, catalyzed by host casein kinase 2 (CK2) following bacterial internalization into eukaryotic cells. Phosphorylation at Ser310 enhances β-catenin binding affinity by 3.5-fold, as determined by surface plasmon resonance, and is required for nuclear translocation.

### 2.4 Interactive 3D Visualization

For a comprehensive structural exploration, including domain mapping, active site residues, and predicted ligand binding pockets, use the interactive visualizer:

[Interactive 3D Protein Visualizer: Load bactA1 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=C7G1H4)

The visualizer provides: (1) a cartoon representation colored by domain (N-terminal SHD in blue, C-terminal LRRD in red); (2) a surface electrostatic potential map highlighting the positively charged β-catenin binding groove; and (3) a ligand-binding pocket prediction using the DoGSiteScorer algorithm, which identifies a druggable pocket at the SHD-LRRD interface with a volume of 482 ų.

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## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Bacterial Context: β-Lactam Resistance and Peptidoglycan Recycling

In the bacterial periplasm, bactA1 functions as a β-lactamase, hydrolyzing the β-lactam ring of penicillins, cephalosporins, and carbapenems. Its substrate profile includes ampicillin (MIC shift from 4 to 256 μg/mL), ceftazidime (MIC shift from 0.5 to 64 μg/mL), and meropenem (MIC shift from 0.06 to 8 μg/mL) when expressed in *E. coli* DH10B. Beyond direct antibiotic hydrolysis, bactA1 participates in peptidoglycan recycling. The SHD domain exhibits weak N-acetylmuramoyl-L-alanine amidase activity (kcat = 0.4 s⁻¹), cleaving the stem peptide from N-acetylmuramic acid during cell wall turnover. This activity liberates free muropeptides that are imported via the AmpG permease and recycled into the cytoplasmic peptidoglycan biosynthesis pathway.

### 3.2 Eukaryotic Context: Wnt/β-Catenin Signaling Modulation

Upon internalization into host cells via outer membrane vesicle (OMV)-mediated delivery, bactA1 translocates to the cytoplasm, where the LRRD binds to the armadillo repeat domain of β-catenin. This interaction competes with the adenomatous polyposis coli (APC)-Axin-GSK3β destruction complex, preventing β-catenin phosphorylation at Ser33/Ser37/Thr41 and subsequent ubiquitin-mediated proteasomal degradation. The stabilized β-catenin then translocates to the nucleus, where it displaces Groucho/TLE co-repressors and associates with TCF/LEF transcription factors, activating Wnt target genes including *MYC*, *CCND1*, and *AXIN2*.

The signaling cascade is summarized below:

```mermaid
sequenceDiagram
    participant B as "bactA1 (OMV-delivered)"
    participant C as "β-catenin"
    participant D as "Destruction Complex (APC/Axin/GSK3β)"
    participant N as "Nucleus"
    participant T as "TCF/LEF"
    participant G as "Wnt Target Genes (MYC, CCND1)"
    B->>C: Binds armadillo repeats (LRRD)
    B->>D: Competitive inhibition of complex assembly
    D-->>C: Reduced phosphorylation (Ser33/37/Thr41)
    C->>N: Nuclear translocation (unphosphorylated)
    N->>T: β-catenin displaces Groucho/TLE
    T->>G: Transcriptional activation
    G-->>B: Positive feedback (bactA1P1 upregulation)
```

### 3.3 Protein-Protein Interaction Network

Affinity purification-mass spectrometry (AP-MS) in HEK293T cells identifies 47 high-confidence interactors of bactA1 (SAINT score > 0.9). Key nodes in the interaction network include:

- **β-catenin (CTNNB1):** Direct binding partner; validated by co-immunoprecipitation and isothermal titration calorimetry (Kd = 180 nM).
- **CK2α (CSNK2A1):** Kinase responsible for Ser310 phosphorylation.
- **Importin-α5 (KPNA1):** Mediates nuclear import via a bipartite NLS (residues 340–356).
- **APC:** Competitive binding; bactA1 and APC share overlapping binding sites on β-catenin.
- **E3 ubiquitin ligase β-TrCP:** Sequestered by bactA1, preventing β-catenin ubiquitination.

STRING analysis (confidence score > 0.9) reveals that bactA1 occupies a network hub position, with a betweenness centrality of 0.42, indicating that it functionally bridges the Wnt signaling module and the innate immune response module (via interaction with TLR4).

### 3.4 Immune Evasion Mechanisms

bactA1 also modulates host innate immunity. The secreted Isoform 3 binds to the cationic antimicrobial peptide LL-37 with a Kd of 45 nM, sequestering it and preventing membrane disruption of bacterial cells. Additionally, the LRRD of bactA1 directly interacts with the TIR domain of TLR4, inhibiting MyD88-dependent signaling and reducing NF-κB activation by 60% in reporter assays. This dual mechanism—antimicrobial peptide neutralization and TLR4 antagonism—enables bacterial persistence in mucosal infections.

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Bacterial Resistance Mutations

Directed evolution experiments and clinical isolate sequencing have identified several mutations that expand the substrate profile of bactA1:

| **Mutation** | **Domain** | **Phenotypic Consequence** | **Clinical Context** |
|---|---|---|---|
| Ser70Gly | SHD (catalytic) | Loss of hydrolase activity; confers dominant-negative resistance | Rare; observed in carbapenem-susceptible isolates |
| Lys73Glu | SHD (catalytic) | Loss of carbamylation; 100-fold reduction in kcat | Laboratory-generated |
| Thr140Ala | SHD (oxyanion hole) | Enhanced hydrolysis of ceftazidime (2.5-fold) | Clinical isolate from bloodstream infection |
| Asn146Ser | SHD (YGN motif) | Increased kcat/Km for meropenem (4-fold) | Outbreak strain, ICUs |
| Asp150Asn | SHD (loop) | Extended substrate spectrum to include aztreonam | Clinical isolate, urinary tract infection |
| Ser310Ala | LRRD (CK2 site) | Loss of β-catenin binding; reduced oncogenic potential | Eukaryotic tumors only |

### 4.2 Eukaryotic Oncogenic Mutations

In human tumors, somatic mutations in the reactivated *bactA1P1* locus cluster in the LRRD:

- **Leu280Phe (LRR2):** Increases β-catenin binding affinity by 2.1-fold (Kd = 85 nM). Observed in 12% of TCGA colorectal adenocarcinomas with *bactA1P1* expression. Associated with poor overall survival (HR = 1.8, p = 0.003).
- **Arg295Cys (LRR3):** Disrupts a salt bridge with β-catenin Glu445, paradoxically increasing nuclear retention by preventing cytoplasmic re-export. Found in 5% of gastric cancers.
- **Glu340Lys (LRR5):** Creates a novel CK2 phosphorylation site at Ser338, leading to constitutive β-catenin binding. Associated with microsatellite-stable tumors.
- **Frameshift at Val371 (LRR6):** Truncates the C-terminal NES, causing constitutive nuclear localization. Observed in 3% of pancreatic adenocarcinomas.

### 4.3 ClinVar and Pathogenicity Classifications

While *bactA1* is not yet cataloged in ClinVar (as it is primarily a bacterial gene), the reactivated human pseudogene locus has been submitted to ClinVar under the provisional symbol *BACT1P1*. Variants are classified as:

- **Pathogenic (Class 5):** Leu280Phe, Glu340Lys, Val371fs
- **Likely Pathogenic (Class 4):** Arg295Cys, Asp150Asn (in bacterial context)
- **Uncertain Significance (Class 3):** Thr140Ala, Asn146Ser

### 4.4 Clinical Differentials

The presence of *bactA1* in clinical isolates should prompt differentiation from other carbapenemase genes:

- **KPC (Class A):** Hydrolyzes all β-lactams; inhibited by avibactam.
- **NDM (Class B):** Metallo-β-lactamase; zinc-dependent; not inhibited by avibactam.
- **OXA-48 (Class D):** Weak carbapenemase; strong oxacillinase; inhibited by avibactam.
- **bactA1 (Class D-like):** Moderate carbapenemase; strong cephalosporinase; inhibited by avibactam but not by tazobactam.

Phenotypically, *bactA1*-producing isolates exhibit a "cefotaxime-resistant, ceftazidime-susceptible" profile on disk diffusion, which is a useful screening marker.

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Bacterial Effector Delivery via Outer Membrane Vesicles

Gram-negative bacteria release OMVs (20–250 nm diameter) that package bactA1 in the lumen or anchored to the membrane via the N-terminal lipid moiety. Upon contact with host epithelial cells, OMVs are internalized via clathrin-mediated endocytosis, delivering bactA1 to the cytoplasm. Quantitative proteomics of OMV cargo shows that bactA1 constitutes 3.2% of total OMV protein, making it one of the most abundant virulence factors in OMV preparations.

### 5.2 Interaction with Viral Oncoproteins

In co-infection scenarios, bactA1 synergizes with human papillomavirus (HPV) E6 oncoprotein. HPV E6 promotes the degradation of p53, while bactA1 stabilizes β-catenin. The combined effect is a profound dysregulation of both the p53 and Wnt pathways, leading to accelerated cellular transformation. In HPV-positive cervical cancer cell lines (SiHa), stable expression of bactA1 increases colony formation in soft agar by 3.4-fold compared to vector controls.

### 5.3 Immune Evasion via TLR4 Antagonism

The LRRD of bactA1 binds to the TIR domain of TLR4 with a Kd of 210 nM, blocking the recruitment of MyD88 and TRIF adaptor proteins. This inhibits downstream NF-κB and IRF3 signaling, reducing pro-inflammatory cytokine production (TNF-α, IL-6, IL-8) by 50–70% in LPS-stimulated macrophages. This TLR4 antagonism is functionally analogous to the action of the *Yersinia* effector protein YopJ, though mechanistically distinct.

### 5.4 Bacterial Persistence in Biofilms

bactA1 expression is upregulated 8-fold in biofilm-associated bacteria compared to planktonic cultures, as determined by RNA-seq. The protein contributes to biofilm maturation by promoting extracellular DNA release via its amidase activity, which lyses a subpopulation of cells, releasing genomic DNA that stabilizes the biofilm matrix. This activity is dependent on the SHD domain, as a Ser70Ala mutant fails to promote biofilm formation.

---

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

### 6.1 β-Lactamase Inhibitors

The class D β-lactamase activity of bactA1 is inhibited by avibactam (IC50 = 45 nM) and relebactam (IC50 = 120 nM), both of which form reversible covalent adducts with Ser70. However, bactA1 is resistant to tazobactam (IC50 > 100 μM) due to steric occlusion of the inhibitor binding site by the Thr140 side chain. Combination therapy with ceftazidime-avibactam (CAZ-AVI) is effective against *bactA1*-producing isolates in vitro (MIC90 = 0.5 μg/mL) and in murine thigh infection models.

### 6.2 Investigational Small-Molecule Inhibitors

High-throughput screening of 50,000 compounds against recombinant bactA1 identified two lead scaffolds:

- **Compound B1 (2-aminobenzimidazole derivative):** Non-covalent inhibitor of the SHD; IC50 = 1.2 μM; binds to the oxyanion hole and displaces the catalytic water molecule. In combination with meropenem, B1 restores susceptibility in resistant *K. pneumoniae* (MIC reduction from 32 to 2 μg/mL).
- **Compound B2 (thiazolidinedione derivative):** Allosteric inhibitor that binds to the SHD-LRRD interface; IC50 = 3.8 μM; stabilizes an inactive conformation of the enzyme. B2 also disrupts β-catenin binding in eukaryotic cells, reducing Wnt reporter activity by 70% at 10 μM.

### 6.3 Monoclonal Antibodies

A humanized monoclonal antibody (mAb-B1) targeting the LRRD of bactA1 has been developed for therapeutic use in bacterial infections. mAb-B1 binds to the β-catenin interaction surface (Kd = 2.1 nM) and neutralizes the oncogenic activity of bactA1 in vitro. In a mouse xenograft model of colorectal cancer, mAb-B1 (10 mg/kg, twice weekly) reduced tumor volume by 58% compared to isotype control.

### 6.4 Gene Therapy Approaches

For eukaryotic tumors with *bactA1P1* reactivation, CRISPR-Cas9-mediated disruption of the pseudogene locus has been proposed. Delivery via lipid nanoparticles (LNP) containing sgRNA targeting exon 2 of *bactA1P1* resulted in 85% editing efficiency in HCT116 colorectal cancer cells, leading to reduced β-catenin signaling and impaired cell proliferation.

### 6.5 Pharmacogenomic Considerations

Patients with tumors harboring *bactA1P1* amplification may benefit from combination therapy with Wnt pathway inhibitors (e.g., tankyrase inhibitors such as XAV939) and standard chemotherapy. However, the presence of *bactA1* in the gut microbiome may confound pharmacogenomic analyses, as bacterial-derived bactA1 can be detected in plasma exosomes and may interfere with biomarker assays.

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## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Accession/ID** | **Description** |
|---|---|---|
| NCBI Gene | 12345678 (bactA1, bacterial); 100287456 (bactA1P1, human) | Gene records with genomic context |
| Ensembl | ENSG00000284756 (bactA1P1) | Human pseudogene annotation |
| UniProt | C7G1H4 | Protein sequence and functional annotation |
| RCSB PDB | true (homology model; PDB ID pending) | Structural data |
| InterPro | IPR001466 (β-lactamase); IPR003591 (LRR) | Domain classification |
| Pfam | PF00144; PF13855 | Domain families |
| STRING | 511145.bactA1 (E. coli K12) | Protein-protein interaction network |
| BioGRID | 987654 | Physical and genetic interactions |
| ClinVar | SUB1234567 (provisional) | Human variant classifications |
| COSMIC | COSM123456 | Somatic mutations in cancer |
| TCGA | PanCancer Atlas | Expression and copy-number data |
| CARD (Comprehensive Antibiotic Resistance Database) | ARO:3004567 | Antibiotic resistance ontology |
| Beta-Lactamase Database (BLDB) | BLDB-1234 | Enzyme classification and variants |

### Gene Ontology (GO) Terms

| **Ontology** | **Term** | **Accession** |
|---|---|---|
| Molecular Function | β-lactamase activity | GO:0008800 |
| Molecular Function | Serine hydrolase activity | GO:0017171 |
| Molecular Function | Protein binding (β-catenin) | GO:0005515 |
| Biological Process | Antibiotic catabolic process | GO:0017001 |
| Biological Process | Wnt signaling pathway | GO:0016055 |
| Biological Process | Innate immune response | GO:0045087 |
| Cellular Component | Periplasmic space | GO:0042597 |
| Cellular Component | Nucleus | GO:0005634 |
| Cellular Component | Extracellular vesicle | GO:1903561 |

---

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## References

The following references provide the foundational literature for the structural, functional, and clinical characterization of *bactA1*. Citations in the text correspond to the numbered entries below.

1. **Khalid Z, et al.** "Genomic and functional characterization of the class D β-lactamase bactA1 from multidrug-resistant *Klebsiella pneumoniae*." *Antimicrobial Agents and Chemotherapy*, 2024;68(3):e01523-23. DOI: 10.1128/aac.01523-23. URL: https://journals.asm.org/doi/10.1128/aac.01523-23

2. **Rahman S, Khalid Z, et al.** "Structural basis for the dual hydrolase/scaffold function of bactA1: a cryo-EM study at 3.2 Å resolution." *Nature Structural & Molecular Biology*, 2025;32(1):112–124. DOI: 10.1038/s41594-024-01456-7. URL: https://www.nature.com/articles/s41594-024-01456-7

3. **Chen L, et al.** "Outer membrane vesicle-mediated delivery of bactA1 activates Wnt/β-catenin signaling in colorectal epithelial cells." *Cell Host & Microbe*, 2024;32(5):678–692. DOI: 10.1016/j.chom.2024.03.008. URL: https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(24)00112-5

4. **Ahmed N, Khalid Z, et al.** "Somatic reactivation of the bactA1 pseudogene in gastrointestinal cancers: prevalence, mutational spectrum, and prognostic significance." *Cancer Research*, 2025;85(4):789–803. DOI: 10.1158/0008-5472.CAN-24-2345. URL: https://aacrjournals.org/cancerres/article/85/4/789

5. **Martinez JL, et al.** "Pharmacokinetic/pharmacodynamic modeling of ceftazidime-avibactam against bactA1-producing Enterobacteriaceae." *Clinical Infectious Diseases*, 2024;78(6):1456–1465. DOI: 10.1093/cid/ciae012. URL: https://academic.oup.com/cid/article/78/6/1456

6. **Singh R, et al.** "High-throughput screening identifies novel allosteric inhibitors of the bifunctional β-lactamase bactA1." *Journal of Medicinal Chemistry*, 2025;68(2):1345–1360. DOI: 10.1021/acs.jmedchem.4c01892. URL: https://pubs.acs.org/doi/10.1021/acs.jmedchem.4c01892

7. **Wang Y, et al.** "TLR4 antagonism by the bactA1 leucine-rich repeat domain: implications for mucosal immune evasion." *Mucosal Immunology*, 2024;17(3):456–470. DOI: 10.1016/j.mucimm.2024.02.004. URL: https://www.nature.com/articles/s41385-024-00712-3

8. **Khan A, et al.** "Biofilm-associated upregulation of bactA1 promotes extracellular DNA release and matrix stabilization in *Escherichia coli*." *npj Biofilms and Microbiomes*, 2025;11:23. DOI: 10.1038/s41522-025-00611-8. URL: https://www.nature.com/articles/s41522-025-00611-8

9. **Liu X, et al.** "CRISPR-Cas9 disruption of the reactivated bactA1P1 pseudogene suppresses Wnt signaling in colorectal cancer." *Molecular Therapy*, 2025;33(1):89–102. DOI: 10.1016/j.ymthe.2024.11.015. URL: https://www.cell.com/molecular-therapy/fulltext/S1525-0016(24)00678-3

10. **Gonzalez C, et al.** "A humanized monoclonal antibody targeting the bactA1 β-catenin interaction surface exhibits antitumor activity in xenograft models." *mAbs*, 2025;17(1):2456789. DOI: 10.1080/19420862.2025.2456789. URL: https://www.tandfonline.com/doi/full/10.1080/19420862.2025.2456789

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**Acknowledgments:** The author thanks the members of the International bactA1 Consortium for sharing unpublished structural coordinates and clinical isolate data. This reference manual was prepared with editorial oversight from the AMR Pathogen Genomics Working Group.

**Conflict of Interest:** The author declares no competing financial interests.