{
  "abstract": "Extended-spectrum β-lactamases (ESBLs), particularly the CTX-M family, have progressively undermined the clinical utility of β-lactam antibiotics. Herein, we identified and characterized a novel CTX-M subgroup designated KLUS, and investigated its taxonomic position and functional properties. Phylogenetic analysis combined with genetic distance calculations supported KLUS as a distinct lineage, with inter-subgroup distances significantly exceeding intra-subgroup distances and distinct clustering (bootstrap support >95%), consistent with the previously established family-wide CTX-M classification. Recombinant plasmids harboring each of the four blaKLUS alleles were constructed in E. coli BL21 (DE3), with optimal expression achieved using 1.0 mM IPTG at 30 °C for 5 h. Minimum inhibitory concentration (MIC) determinations revealed that KLUS-1 through KLUS-3 conferred high-level resistance to ampicillin and ceftriaxone, moderate resistance to cefotaxime, and minimal resistance to ceftazidime (MIC < 0.125 μg/mL). KLUS-4 exhibited enhanced ceftazidime resistance (MIC = 8 μg/mL) and a reduced inhibitor response at the phenotypic level (a 16-fold reduction of the cefotaxime MIC with clavulanic acid, in contrast to KLUS-1, where clavulanic acid reduced the MIC to <0.015 μg/mL). β-lactamase inhibitors reduced cefotaxime MICs far exceeding 16-fold in KLUS-1 through KLUS-3, consistent with ESBL phenotypes. Steady-state kinetic analyses demonstrated subtype-dependent catalytic efficiencies that were highest for ampicillin and penicillin G in KLUS-2/3/4 and for ceftriaxone in KLUS-1, broadly consistent with MIC results. The substantially lower catalytic efficiency for ceftazidime may explain its reduced resistance phenotype. Structural modeling revealed that KLUS enzymes comprise 11 α-helices and 5 β-sheets, with a conserved catalytic cavity and SDN loop. Twenty-three unique amino acid substitutions distinguish KLUS from CTX-M-2. V77I (pre-protein positions 106) is located proximal to the Ω-loop region, and any functional contribution of this conservative substitution remains speculative. These findings expand the known diversity of CTX-M β-lactamases; the clinical significance of KLUS requires further investigation in clinical isolates.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Original Research",
  "arxiv": null,
  "author_total": 9,
  "authors": [
    {
      "name": "Zhenzhou Huang"
    },
    {
      "name": "Jun Li"
    },
    {
      "name": "Xiao Liu"
    },
    {
      "name": "Lingyi Zeng"
    },
    {
      "name": "Zhibei Zheng"
    },
    {
      "name": "Hua Yu"
    },
    {
      "name": "Duochun Wang"
    },
    {
      "name": "Keyi Yu"
    },
    {
      "name": "Junfang Chen"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0g7b1rtvfhxae.bib",
  "cited_by": 0,
  "doi": "10.3389/fmicb.2026.1997337",
  "fulltext_url": null,
  "id": "0g7b1rtvfhxae",
  "issns": [
    "1664-302X"
  ],
  "landing_url": "https://www.frontiersin.org/articles/10.3389/fmicb.2026.1997337",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "feed-journal",
      "biology/microbiology"
    ]
  ],
  "openalex": null,
  "pdf_url": null,
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-30",
  "publisher": "Frontiers Media SA",
  "ris": "https://research.draconitic.com/paper/0g7b1rtvfhxae.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:18Z",
      "native_id": "10.3389/fmicb.2026.1997337",
      "source": "feed-frontiers",
      "url": "https://www.frontiersin.org/articles/10.3389/fmicb.2026.1997337"
    },
    {
      "first_seen": "2026-10-30T12:19:12Z",
      "native_id": "10.3389/fmicb.2026.1997337",
      "source": "crossref",
      "url": "https://www.frontiersin.org/articles/10.3389/fmicb.2026.1997337/full"
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  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "feed-journal:biology/microbiology",
      "subfield": "microbiology"
    }
  ],
  "title": "Genetic, biochemical, and structural characterization of a novel KLUS subgroup of CTX-M-type extended-spectrum β-lactamases reveals an evolutionarily distinct lineage with unique functional properties",
  "title_text": "Genetic, biochemical, and structural characterization of a novel KLUS subgroup of CTX-M-type extended-spectrum β-lactamases reveals an evolutionarily distinct lineage with unique functional properties",
  "type": "peer-reviewed",
  "updated_at": "2026-11-01T00:20:56Z",
  "url": "https://research.draconitic.com/paper/0g7b1rtvfhxae",
  "venue": "Frontiers in Microbiology",
  "versions": []
}