An affinity selection–mass spectrometry method for the identification of small molecule ligands from self-encoded combinatorial librariesDiscovery of a novel antagonist of E. coli dihydrofolate reductase

Screening assays using target-based affinity selection coupled with high-sensitivity detection technologies to identify small-molecule hits from chemical libraries can provide a useful discovery approach that complements traditional assay systems. Affinity selection-mass spectrometry (AS-MS) is one such methodology that holds promise for providing selective and sensitive high-throughput screening platforms. Although AS-MS screening platforms have been used to discover small-molecule ligands of proteins from many target families, they have not yet been used routinely to screen integral membrane proteins. The authors present a proof-of-concept study using size exclusion chromatography coupled to AS-MS to perform a primary screen for small-molecule ligands of the purified muscarinic M2 acetylcholine receptor, a G-protein-coupled receptor. AS-MS is used to characterize the binding mechanisms of 2 newly discovered ligands. NGD-3350 is a novel M2-specific orthosteric antagonist of M2 function. NGD-3366 is an allosteric ligand with binding properties similar to the allosteric antagonist W-84, which decreases the dissociation rate of N-methyl-scopolamine from the M2 receptor. Binding properties of the ligands discerned from AS-MS assays agree with those from in vitro biochemical assays. The authors conclude that when used with appropriate small-molecule libraries, AS-MS may provide a useful high-throughput assay system for the discovery and characterization of all classes of integral membrane protein ligands, including allosteric modulators.

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MALDI-TOF-Based Affinity Selection Mass Spectrometry for Automated Screening of Protein–Ligand Interactions at High Throughput

SLAS DISCOVERY Advancing Life Sciences ◽

10.1177/2472555220959266 ◽

2020 ◽

Vol 26 (1) ◽

pp. 44-57

Author(s):

Roman P. Simon ◽

Martin Winter ◽

Carola Kleiner ◽

Lucie Wehrle ◽

Michael Karnath ◽

...

Keyword(s):

Mass Spectrometry ◽

Small Molecule ◽

High Throughput ◽

Binding Assay ◽

Size Exclusion ◽

Affinity Selection ◽

Maldi Tof ◽

Protein Ligand Interactions ◽

Small Molecule Ligands ◽

Ligand Interactions

Demonstration of in vitro target engagement for small-molecule ligands by measuring binding to a molecular target is an established approach in early drug discovery and a pivotal step in high-throughput screening (HTS)-based compound triaging. We describe the setup, evaluation, and application of a ligand binding assay platform combining automated affinity selection (AS)-based sample preparation and label-free matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis. The platform enables mass spectrometry (MS)-based HTS for small-molecule target interactions from single-compound incubation mixtures and is embedded into a regular assay automation environment. Efficient separation of target–ligand complexes is achieved by in-plate size exclusion chromatography (SEC), and small-molecule ligands are subsequently identified by MALDI-TOF analysis. In contrast to alternative HTS-capable binding assay formats, MALDI-TOF AS-MS is capable of identifying orthosteric and allosteric ligands, as shown for the model system protein tyrosine phosphatase 1B (PTP1B), irrespective of protein function. Furthermore, determining relative binding affinities (RBAs) enabled ligand ranking in accordance with functional inhibition and reference data for PTP1B and a number of diverse protein targets. Finally, we present a validation screen of more than 23,000 compounds within 24 h, demonstrating the general applicability of the platform for the HTS-compatible assessment of protein–ligand interactions.

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