Structure and allostery in major facilitator superfamily symport mechanisms

Guan, L.

doi:10.1107/S2059798326007485

Figure 1
Structures of MelB_St. (a) Crystal structure of the sugar-bound outward-facing conformation of the MelB_St D59C uniporter mutant at a resolution of 2.60 Å (PDB entry 9old). The bound α-nitrophenyl galactoside (α-NPG, pink) interacts with MelB_St at the apex of the outward-facing cavity and in the middle of the protein. The α-NPG-binding residues are highlighted as sticks. (b) CryoEM structure of the Na⁺-bound inward-facing conformation of WT MelB_St (PDB entry 8t60). The structure was solved as a complex with a conformation-specific nanobody Nb725_4 and a fiducial NabFab. The bound Na⁺ is shown as a pink sphere and the binding residues are highlighted as sticks. The membrane sidedness is indicated. (c) Sugar recognition pocket. Crystal structures of four α-sugars with different numbers of sugar units. All sugars are colored yellow, and the binding pocket contributed by the N- and C-terminal domains is colored green and blue, respectively. (d) Four well aligned bound sugar molecules. The four crystal structures shown in (a) were overlaid and the bound sugar structures are displayed with identical color codes. The carbon positions for the galactosyl and glucosyl moieties of melibiose are labeled C1–C6 and C1′–C6′, respectively. This panel was modified from Figs. 2 and 4(e) of Hariharan et al. (2026

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STRUCTURAL
BIOLOGY

ISSN: 2059-7983

Volume 82| Part 9| September 2026| Pages 1030-1043

https://doi.org/10.1107/S2059798326007485

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