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Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2026,2,3]]},"abstract":"<jats:p>Alpha-synuclein (\u03b1S) plays a central role in several neurodegenerative diseases. Although predominantly neuronal, \u03b1S is also present in peripheral fluids such as serum and cerebrospinal fluid (CSF), where it may contribute to disease propagation. However, its extracellular interactions remain poorly understood. By combining in situ NMR spectroscopy and bottom\u2013up MS proteomics, we reveal that monomeric \u03b1S exhibits distinct interactomes in serum versus CSF. Both N- and C-terminal \u03b1S regions bind to serum components, while in CSF, \u03b1S remains largely unbound. The N- and C-terminal interactions are mechanistically diverse: C-terminal binding is electrostatic, whereas N-terminal interactions persist under high ionic strength, implicating hydrophobic interactions. Deletion of the first ten N-terminal residues, which include several hydrophobic side chains, abolishes these interactions, highlighting their functional importance. Proteomic profiling and NMR validation identify key \u03b1S serum partners, including albumin, \u03b3-globulins, and lipoproteins, which, together, are sufficient to recapitulate the serum \u03b1S interactome and elicit redundant interactions with the \u03b1S N-terminal region. Despite such redundancy, \u03b1S methionine oxidation selectively disrupts N-terminal binding, suggesting a redox-sensitive mechanism regulating the \u03b1S extracellular interactome. Notably, C-terminal interactions are preserved when the N-terminal binding is detuned, indicating that the N- and C-termini elicit independent interactions with the extracellular matrix, a marked difference from the intracellular milieu. These findings uncover dynamic and fluid-specific \u03b1S interaction signatures, offering new molecular insights into its peripheral roles and identifying potential new epitopes as synucleinopathy biomarkers. These results are also relevant for other amyloidogenic intrinsically disordered proteins (IDPs), for which \u03b1S serves as a prototype.<\/jats:p>","DOI":"10.1073\/pnas.2521639123","type":"journal-article","created":{"date-parts":[[2026,1,28]],"date-time":"2026-01-28T16:58:41Z","timestamp":1769619521000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":0,"title":["In situ NMR and integrative proteomics reveal the interaction signature of serum \u03b1-synuclein"],"prefix":"10.1073","volume":"123","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6342-8536","authenticated-orcid":false,"given":"Jinfeng","family":"Huang","sequence":"first","affiliation":[{"name":"Department of Chemistry and Chemical Biology, McMaster University","place":["Hamilton, Canada"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rashik","family":"Ahmed","sequence":"additional","affiliation":[{"name":"Program in Molecular Medicine, Hospital 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