Structural insights into a conserved mechanism of choline translocation through CHT.

Abstract

Choline is an essential nutrient critical for cellular homeostasis across all domains of life. In humans, choline uptake in cholinergic neurons for its recycling into acetylcholine is mediated by the high-affinity Na⁺-dependent transporter SLC5A7 (CHT1). Prokaryotes also depend on choline as an osmo-protectant and as metabolite, raising the possibility that bacteria also have choline transporters akin to CHT1. Here, we identify and characterize a bacterial Na⁺-dependent choline transporter (sfCHT) with high sequence identity to CHT1. Cryo-EM structures of Na⁺- and choline-bound sfCHT reveal a LeuT-fold architecture with Na⁺ coordination geometry similar to CHT1. Captured in an inward-facing conformation, in sfCHT choline is found at a site near the cytoplasmic side. Computational analysis and transport assays of sfCHT and CHT1 variants reveal local conformational rearrangements in conserved residues along a defined pathway to the cytosolic site. These findings provide structural and mechanistic insights into intracellular choline transition, suggesting an evolutionarily conserved mechanism between the bacterial and human choline transporters.