9F84

Structure of Choline O-acetyltransferase in complex with 1-Methyl-4-[2-(1-naphthyl)-2-(propylthio)ethyl]pyridinium at 1.9 Angstrom resolution

This is a non-PDB format compatible entry.

Summary for 9F84

• Entry DOI: 10.2210/pdb9f84/pdb
• Descriptor: Choline O-acetyltransferase, 1-methyl-4-[(2S)-2-naphthalen-1-yl-2-propylsulfanyl-ethyl]-4H-pyridine, SODIUM ION, ... (4 entities in total)
• Functional Keywords: chat, complex, inhibitor, reversible, transferase
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 1
• Total formula weight: 68459.84

Authors

Forsgren, N.,Ekstrom, F. (deposition date: 2024-05-06, release date: 2025-05-21, Last modification date: 2026-06-03)

Primary citation

Forsgren, N.,Jonsson, F.,Carlsson, M.,Sander, R.A.,Larsson, A.,Linden, P.,Linusson, A.,Engdahl, C.S.,Wiktelius, D.,Ekstrom, F.
Analysis of ligand recognition by choline-O-acetyltransferase reveals thiol-reactive assay interference and weak ligand affinity in solution.
J.Biol.Chem., :113115-113115, 2026

PubMed Abstract: Choline O-acetyltransferase (ChAT) catalyzes the biosynthesis of acetylcholine and is a cysteine-rich enzyme that has been investigated using a range of biochemical and structural approaches. Existing ChAT ligands rely on electrophilic or unstable scaffolds that limit their suitability for biological systems. Prior work established that arylvinylpyridiniums (AVPs) are substrate mimics that undergo ChAT-catalyzed hydrothiolation with CoA to form covalent AVP-CoA adducts. Here, we applied a structure-guided strategy to design non-reactive ligands intended to mimic key features of the AVP-CoA binding pose while avoiding covalent reactivity. Nineteen analogs were synthesized and evaluated across complementary biochemical, structural, and biophysical assays. X-ray crystallography confirmed that the new ligands bind within the ChAT tunnel similar to AVP-CoAs. Importantly, the high cysteine content of ChAT, especially within a reactive CXCXXC motif, rendered the enzyme susceptible to modification by the widely used 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM) reagent used for measuring ChAT activity, leading to confounding results in thiol-dependent activity assays. Enzyme-free counter-screens demonstrated that all apparent inhibitory activity arose from interference with assay readout rather than true enzymatic inhibition. Surface plasmon resonance measurements established that none of the designed ligands display detectable reversible affinity for ChAT, despite their crystallographically validated poses, and no selectivity over the related enzyme carnitine-O-acetyltransferase (CrAT) was observed. These findings demonstrate that confirmed binding with X-ray crystallography is insufficient to confer functional interaction with ChAT and highlight the susceptibility of this enzyme to thiol-reactive assay artefacts. More broadly, this work underscores the necessity of integrating orthogonal biophysical validation when studying ligand binding to cysteine-rich enzymes.

PubMed: 42103233
DOI: 10.1016/j.jbc.2026.113115

Experimental method

X-RAY DIFFRACTION (1.9 Å)