Assessing Squarates as Amine-Reactive Probes
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nihms-1968453.pdf
Description
Accepted version
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638.19 KB
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Author(s)
Taylor, Katherine I
Ho, Jordan S
Trial, Hallie O
Carter, Alan W
Kiessling, Laura L
Date Issued
November 8, 2023
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Citation
Katherine I. Taylor, Jordan S. Ho, Hallie O. Trial, Alan W. Carter, Laura L. Kiessling; Assessing Squarates as Amine-Reactive Probes. Journal American Chemical Society 22 November 2023; 145 (46): 25056–25060.
Version
Author's final manuscript
Abstract
Probes that covalently label protein targets facilitate the identification of ligand-binding sites. Lysine residues are prevalent in the proteome, making them attractive substrates for covalent probes. However, identifying electrophiles that undergo amine-specific, regioselective reactions with binding site lysine residues is challenging. Squarates can engage in two sequential conjugate addition–elimination reactions with amines. Nitrogen donation reduces the second reaction rate, making the mono squaramide a mild electrophile. We postulated that this mild electrophilicity would demand a longer residence time near the amine, affording higher selectivity for binding site lysines. Therefore, we compared the kinetics of squarate and monosquaramide amine substitution to alternative amine bioconjugation handles. The data revealed that N-hydroxy succinimidyl esters react 4 orders of magnitude faster, consistent with their labeling promiscuity. Squarate reactivity can be tuned by a substitution pattern. Electron-withdrawing groups on the vinylogous ester or amide increase reaction rates. Dithionosquarates react more rapidly than squarates, while vinylogous thioester analogs, dithiosquarates, react more slowly. We assessed squarate selectively using the UDP-sugar processing enzyme GlfT2 from Mycobacterium tuberculosis, which possesses 21 surface-exposed lysines. The reaction predominately modified one lysine proximal to a binding site to afford covalent inhibition. These findings demonstrate the selectivity of squaric esters and squaramides, which is a critical feature for affinity-based chemoproteomic probes.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1021/jacs.2c05691
