Structure and allostery in major facilitator superfamily symport mechanisms

Guan, L.

doi:10.1107/S2059798326007485

Figure 6
Mapping of HDX of MelB_St in the absence or presence of melibiose and/or Na⁺. (a) Deuterium map of apo MelB_St. Mean deuteriation levels of MelB_St peptides in the apo state are presented against the amino-acid sequence. The lengths of the red bars correspond to the peptide lengths, and the white background indicates noncovered positions. Peptides covering sugar- and cation-binding sites and the cytoplasmic gating salt-bridge network are highlighted by boxes and labeled individually. (b) Mapping of ligand effects of HDX on a topology model of MelB_St. Melibiose- and Na⁺-binding residues are labeled in green or black, respectively, and residues in the cytoplasmic gating salt-bridge network are labeled in white. Residues in pink at the sugar-binding pocket or on magenta backgrounds in the cytoplasmic gating salt-bridge network indicate higher deuteriation levels in the apo state with significant ligand-induced protection. Residues on a blue background indicate peptides with low levels of deuteriation in the apo state with no significant ligand effects. Arg363 is a noncoverage position. (a) and (b) were modified from Figs. 5(a) and 8(c), respectively, of Hariharan et al. (2026

). (c) Melibiose-induced differential HDX mapping on structures of MelB_St. Left and right columns, melibiose effects on HDX of MelB_St in the absence or presence of Na⁺, respectively. Upper rows, a side view of the α-NPG-bound outward-facing structure (PDB entry 9olp) with helix V or II at the front, respectively, as labeled. Lower row, the same structure was aligned with the inward-facing structure (PDB entry 8t60) in cyan and rotated 90° around the membrane plane. Overlapping peptides in red or blue indicate deprotection or protection, respectively. Loops are colored red. The purple-colored peptide indicates deprotection at the 30 s time point and protection at the 3000 s time point. The displacement of loop_1–2 and loop_11–12 between the inward- and outward-facing conformations is indicated by arrows.

STRUCTURAL
BIOLOGY

ISSN: 2059-7983

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

https://doi.org/10.1107/S2059798326007485

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