We report how solution pH can impact the interpretation of aSyn HSQC NMR spectra and demonstrate that small-molecule formulations (e.g., complexation with acidic salts) can lower sample pH and confound interpretation of drug binding and concomitant protein structural changes. N2 - 1H,15N-Heteronuclear Single Quantum Coherence (HSQC) NMR is a powerful technique that has been employed to characterize small-molecule interactions with intrinsically disordered monomeric α-Synuclein (aSyn). (NINDS 1R01NS117968) and National Institutes of Health Chemistry–Biology Interface Training Grant to C.R.B. This study was supported by US National Institutes of Health to J.N.S. The authors disclose receipt of the following financial support for the research, authorship, and/or publication of this article. T1 - pH Effects Can Dominate Chemical Shift Perturbations in 1H,15N-HSQC NMR Spectroscopy for Studies of Small Molecule/α-Synuclein InteractionsĪll NMR experiments were performed at the Minnesota NMR facility (MNMR). Previously, DOPA-aSyn interactions have been shown to elicit a dramatic chemical shift perturbation (CSP) localized to aSyns preferential interaction with aSyn under acidic pH represents a novel understanding of DOPA-aSyn interactions that may provide insight into the potential gain of toxic function of aSyn misfolding in α-synucleinopathies.", Through stringent pH control, we confirm that several previously identified compounds (EGCG, Baicalin, and Dopamine (DOPA)) as well as a series of potent small-molecule inhibitors of aSyn pathology (Demeclocycline, Ro90-7501, and (±)-Bay K 8644) are capable of direct target engagement of aSyn. Furthermore, DOPA’s preferential interaction with aSyn under acidic pH represents a novel understanding of DOPA-aSyn interactions that may provide insight into the potential gain of toxic function of aSyn misfolding in α-synucleinopathies.Ībstract = "1H,15N-Heteronuclear Single Quantum Coherence (HSQC) NMR is a powerful technique that has been employed to characterize small-molecule interactions with intrinsically disordered monomeric α-Synuclein (aSyn). These results suggest that previous interpretations of DOPA-aSyn interactions were conflated with pH-induced CSP, highlighting the need for stringent pH control to minimize potential false-positive interpretations of ligand interactions in HSQC NMR experiments. In contrast, under tightly controlled pH 5.0, DOPA induces significant CSPs observed at both ionizable and nonionizable residues. Interestingly, this CSP profile mirrors our pH titration, where a small reduction in pH affects H50 CSP, and large pH changes induce robust C-terminal CSP. Previously, DOPA-aSyn interactions have been shown to elicit a dramatic chemical shift perturbation (CSP) localized to aSyn’s H50 at low DOPA concentrations then expanding to aSyn’s acidic C-terminal residues at increasing DOPA levels. 1H, 15N-Heteronuclear Single Quantum Coherence (HSQC) NMR is a powerful technique that has been employed to characterize small-molecule interactions with intrinsically disordered monomeric α-Synuclein (aSyn).
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