{
  "abstract": "Background. Alternative oxidase (AOX) is a mitochondrial terminal oxidase that provides an alternative route for electron transfer, contributing to respiratory flexibility and redox homeostasis under stress conditions. In trypanosomatids, AOX displays a highly uneven distribution associated with extensive diversification of mitochondrial electron transport chains (ETCs). In addition to canonical AOX, many trypanosomatids encode an enigmatic AOX-like protein (AOX-L), whose evolutionary origin and functional significance remain unresolved. Results. Here, we investigated the evolutionary distribution, phylogenetic relationships, structural conservation, and functional divergence of AOX and AOX-L across euglenozoans. Comparative genomic analyses revealed a patchy distribution of both proteins among kinetoplastids, with multiple independent losses during evolution. Phylogenetic analyses demonstrated that AOX and AOX-L represent distinct evolutionary lineages, indicating independent origins rather than duplication-derived divergence. While AOX showed a conserved eukaryotic origin, AOX-L occupied a separate phylogenetic position and lacked key residues required for ubiquinol oxidation. Structural modelling revealed that AOX-L retained the characteristic AOX fold, predicted membrane association, and dimeric organization, but lacked the catalytic architecture necessary for enzymatic activity. Transcriptomic and biochemical analyses of four AOX-containing trypanosomatid species showed that AOX expression and activity correlated with mitochondrial ETC organization. Species lacking cytochrome-dependent complexes III and IV displayed substantially higher AOX expression and enzymatic activity, consistent with AOX functioning as the primary terminal oxidase in these lineages. Conversely, species retaining a canonical ETC exhibited lower AOX activity, suggesting a role in metabolic flexibility and redox regulation. Conclusions. Our study provides a comprehensive evolutionary and functional framework for alternative oxidases in trypanosomatids. We demonstrate that AOX and AOX-L are evolutionarily distinct proteins with different predicted functions: AOX maintains respiratory electron flow according to lineage-specific mitochondrial requirements, whereas AOX-L represents a structurally conserved but catalytically inactive protein family that may have acquired an alternative regulatory role. These findings highlight how mitochondrial respiratory components diversify during eukaryotic evolution and provide a basis for future investigations into the biological function of AOX-L.",
  "abstract_shown": true,
  "affiliations": [
    "University of Ostrava: Ostravska univerzita"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 9,
  "authors": [
    {
      "name": "K. Zahonova"
    },
    {
      "name": "O. Gahura"
    },
    {
      "name": "K. Benedikova"
    },
    {
      "name": "N. Trusina"
    },
    {
      "name": "E. Kalita"
    },
    {
      "name": "L. Chmelova"
    },
    {
      "name": "I. Skodova-Sverakova"
    },
    {
      "name": "A. Zikova"
    },
    {
      "affs": [
        0
      ],
      "name": "V. Yurchenko"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9z4qm5h48by11.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.27.754813",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.09.27.754813v1.full",
  "id": "9z4qm5h48by11",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.09.27.754813v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "biochemistry"
    ],
    [
      "openalex",
      "2713|Trypanosoma species research and implications"
    ]
  ],
  "openalex": "W7214668208",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.09.27.754813v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-27",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9z4qm5h48by11.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:54Z",
      "native_id": "10.64898/2026.09.27.754813",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.09.27.754813v1"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "openalex:2713|Trypanosoma species research and implications",
      "subfield": "epidemiology-public-health"
    }
  ],
  "title": "Alternative oxidase in trypanosomatids",
  "title_text": "Alternative oxidase in trypanosomatids",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:54Z",
  "url": "https://research.draconitic.com/paper/9z4qm5h48by11",
  "venue": "bioRxiv",
  "versions": []
}