{
  "abstract": "Background: Protein-protein interactions enable viruses to adapt and replicate by modifying host factors. Thermodynamic characterization of viral-host complexes can reveal viral mechanisms, broader principles of protein interactions, and properties relevant to anti-HIV-1 inhibitor development. Here, we examine the binding of the HIV-1 matrix (MA) protein to host calmodulin (CaM). MA, the N-terminal domain of Gag (group-specific antigen), directs Gag to the plasma membrane for viral assembly and maturation and may recruit CaM to facilitate this trafficking. However, the MA-CaM interaction remains poorly characterized. MA contains a noncanonical N-terminal CaM-binding motif with hydrophobic regions that may mediate CaM binding and a central, positively charged KKK cluster. Objective: We aimed to determine the binding affinities of MA to calcium-bound CaM (Ca2+-CaM), elucidate protein regions that are critical to the heterocomplex formation, and monitor the conformational alterations in Ca2+-CaM upon binding to MA. Methods: We studied Ca2+-CaM binding to synthetic MA peptides representing full-length wild type (FL WT), a C-terminal truncation lacking the KKK cluster, and an FL K26N/K27H/K28Q triple mutant of the MA CaM-binding motif. The peptides were C-terminally labeled with Cy3, and FL CaM S39C with Cy5. Binding affinity was measured by ensemble Forster resonance energy transfer (eFRET) using 100 nM Cy3-MA and increasing Cy5-Ca2+-CaM concentrations in the range of 50 nM to 2.5 microM. Conformational changes in doubly spin-labeled Ca2+-CaM upon MA binding were probed by double electron-electron resonance (DEER) spectroscopy. Results: Cy3 quenching and FRET analyses of complexes with Cy5-Ca2+-CaM yielded dissociation constants of ~80 nM for FL WT MA, ~65 nM for the truncation, and ~250 nM for the triple mutant, with corresponding binding free energies of ~9.8 to ~9 kcal/mol. These values indicate stable, specific complexes and show that the KKK cluster contributes little to MA-Ca2+-CaM binding. DEER measurements of Ca2+-CaM labeled at S39C and A103C showed that FL WT MA binding shifted the ~5.3 nm interspin distance of extended Ca2+-CaM to a broader ~1.8-3 nm distribution, indicating a major CaM restructuring. Conclusion: These findings define key energetic and structural features of MA-Ca2+-CaM interactions and clarify how HIV-1 proteins exploit CaM.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 6,
  "authors": [
    {
      "name": "Arvin Saffarian Delkhosh"
    },
    {
      "name": "Adeyemi Ogunbowale"
    },
    {
      "name": "Elaheh Hadadianpour"
    },
    {
      "name": "Kazi Mustafa Mahmud"
    },
    {
      "name": "Peter P. Borbat"
    },
    {
      "name": "Elka R. Georgieva",
      "orcid": "0000-0001-9980-5260"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/dqnsznge3y5gd.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.10.19.760223",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.10.19.760223v1.full",
  "id": "dqnsznge3y5gd",
  "issns": [
    "2692-8205"
  ],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.10.19.760223v1",
  "language": "en",
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "biophysics"
    ],
    [
      "heading",
      "Article"
    ],
    [
      "openalex",
      "2406|HIV Research and Treatment"
    ]
  ],
  "openalex": "W7223467694",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.10.19.760223v1.full.pdf",
  "pmcid": "PMC13738617",
  "pmid": "42996055",
  "published": "2026-10-19",
  "publisher": "Cold Spring Harbor Laboratory Preprints",
  "ris": "https://research.draconitic.com/paper/dqnsznge3y5gd.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:32Z",
      "native_id": "10.64898/2026.10.19.760223",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.10.19.760223v1"
    },
    {
      "first_seen": "2026-11-09T12:23:35Z",
      "native_id": "PMC13738617",
      "source": "pmc",
      "url": "https://doi.org/10.64898/2026.10.19.760223"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "biorxiv:biophysics",
      "subfield": "biophysics"
    }
  ],
  "title": "Affinity and Conformations of Ca2+-Calmodulin Bound to Peptides Containing the Calmodulin-Binding Motif of HIV-1 Matrix Protein",
  "title_text": "Affinity and Conformations of Ca2+-Calmodulin Bound to Peptides Containing the Calmodulin-Binding Motif of HIV-1 Matrix Protein",
  "type": "preprint",
  "updated_at": "2026-11-09T12:23:35Z",
  "url": "https://research.draconitic.com/paper/dqnsznge3y5gd",
  "venue": "bioRxiv",
  "versions": []
}