Volume 278, May 2026, 113229Author links open overlay panel, , , , , , , Highlights•

Acetylation of α-synuclein affects the chemical properties of the high-affinity Cu site.

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Cu(I) binds to thiethers of Met1 and Met5 and Asp2 carboxylate; the fourth ligand is key.

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Acetylated α-synuclein uses acetyl carbonyl; α-synuclein uses the N-term for Cu(I) bindingaa.

Abstract

Amyloid aggregation of alpha-synuclein (AS) protein is associated with Parkinson's disease. Physiologically, AS plays a crucial role in the uptake, storage, and recycling of neurotransmitter vesicles. AS has three independent binding sites for Cu(II) and Cu(I) ions. N-terminal acetylation of AS impacts the highest-affinity site of Cu, encompassing the first five residues; it prevents Cu(II) coordination, enhances Cu(I) binding affinity, raises its redox potential, and extends the α-helix to the first ten residues. In this study, X-ray absorption spectroscopy and electronic structure calculations are employed to provide a detailed molecular description of the highest affinity Cu(I) binding site in AS, both in the acetylated AS (AcAS) and non-acetylated forms of the protein. The roles of methionine residues Met1 and Met5 in Cu(I) binding are also evaluated using peptide fragment models. Our findings indicate that in both cases, the coordination sphere is tetracoordinated, with the two sulfur atoms from Met1 and Met5 serving as the primary anchors for Cu(I) coordination. At the same time, Met1 plays a crucial role in stabilizing Cu(I). While both complexes include the carboxylate oxygen of Asp2, a key difference lies in the fourth ligand: the Cu(I)-AS complex utilizes the N-terminal group, whereas the Cu(I)-AcAS complex uses a carbonyl oxygen from the N-terminal acetyl group. These results provide deeper insights into how acetylation impacts the chemical properties of the high-affinity copper binding site in AS and contribute to a better understanding of the role of Cu(I) binding in the physiological function of AS.

Graphical abstract

Synopsis for the Graphical Abstract

X-ray absorption spectroscopy and electronic structure calculations reveal molecular differences in the highest affinity Cu(I) binding site in α-synuclein (AS) and its acetylated form AcAS. Met1 and Met5 sulfur atoms anchor the tetracoordinated Cu(I). Acetylation changes the fourth ligand: AS uses the N-terminus; AcAS uses the acetyl carbonyl.Download: Download high-res image (44KB)Download: Download full-size imageKeywords

Alpha synuclein

Acetylation

Copper coordination

Parkinson's disease

X-ray spectroscopy

DFT

AbbreviationsAcAS

Acetylated form of alpha-synuclein

AcAS(1–6)

Acetylated form of peptide (1–6) of alpha-synuclein

AcASH50A

Acetylated form of alpha-synuclein with His50 to Ala50 mutation

AS(1–6)

Peptide (1–6) of alpha-synuclein

ASH50A

Alpha-synuclein with His50 to Ala50 mutation

Buffer A

20 mM MES buffer with 100 mM NaCl and 50% glycerol

DFT

Density Functional Theory

EPR

Electron Paramagnetic Resonance

EXAFS

Extended X-ray absorption fine structure

NAC

Non-amyloid component region of alpha-synuclein protein

NMR

Nuclear Magnetic Resonance

XANES

X-ray absorption near-edge structure

XAS

X-ray absorption spectroscopy

© 2026 The Authors. Published by Elsevier Inc.