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bioRxiv · 10.1101/2025.07.28.667264

CH···S hydrogen bonds drive molecular recognition of ergothioneine by the microbial transporter

Legg, K. A.·Gonzalez-Gutierrez, G.·Edmonds, K. A.·Shushkov, P. G.·Giedroc, D. P.
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Abstract

Many bacteria harbor an ATP-binding cassette (ABC) transporter named EgtU specific for the human dietary antioxidant and 2-thioimidazole-containing low molecular weight thiol ergothioneine (ET). How the solute binding domain, EgtUC, discriminates among ET and other similar molecules is unknown. Here, we use a "chimeric" mutagenesis strategy and two distantly related EgtUCs from Streptococcus pneumoniae and Helicobacter pylori to show that a suite of EgtUC alkyl CH***S hydrogen bonds to the ET thione S atom are central determinants of molecular recognition. Small perturbations in CH***S distance and angle give rise to sharply attenuated transport-competent ET-bound "closed" state lifetimes and increased motional disorder in the binding pocket, not around the S atom itself, but distally in weakening NH***O hydrogen bonds. This is, to our knowledge, the first work to describe the impact of alkyl CH***S H-bonding in a biological protein-ligand complex in water.

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Legg, K. A., Gonzalez-Gutierrez, G., Edmonds, K. A., Shushkov, P. G., Giedroc, D. P.. 2025-07-31. CH···S hydrogen bonds drive molecular recognition of ergothioneine by the microbial transporter. https://doi.org/10.1101/2025.07.28.667264

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