Download MendeleyStructural insights into xyloglucan recognition by an ABC transporter from a Gram-positive, thermophilic bacterium.
Tjo, H., Jiang, V., Jeffrey, P.D., Zhu, A., Link, A.J., Joseph, J.A., Conway, J.M.(2026) FEBS J
- PubMed: 42545829 Search on PubMed
- DOI: https://doi.org/10.1111/febs.70667
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9PMY - PubMed Abstract:
Xyloglucan (an α-1,6-xylosyl-substituted β-1,4-glucan) is a major hemicellulose of the primary cell wall of many plants and an important growth substrate for biomass-degrading bacteria in diverse ecological niches, including the gut microbiome and hot springs. In Gram-positive bacteria, xyloglucan is deconstructed into soluble oligosaccharides in the extracytoplasmic space before import by ATP-Binding Cassette (ABC) transporters, but the structural basis for this process remains poorly understood. Here, we identified an ABC transporter for xyloglucan uptake (Athe_2052-2054) in the Gram-positive, plant biomass-degrading thermophile Anaerocellum bescii, which is conserved across the Anaerocellum genus. We solved the apo crystal structure of its extracellular substrate-binding protein (SBP), Athe_2052, revealing a unique tertiary fold found only in a small subset of SBPs that bind complex oligosaccharides. To our knowledge, Athe_2052 is the first structurally characterized ABC SBP known to recognize xyloglucan oligosaccharides. Biophysical analysis showed that while Athe_2052 binds unsubstituted β-glucan chains, recognition of xyloglucan side chains in the binding pocket markedly increases affinity (K d = 14 nm) for xyloglucan heptasaccharide (XXXG), the principal oligosaccharide released during xyloglucan deconstruction. Molecular modeling revealed that xyloglucan heptasaccharide, owing to its branched substitutions, is bound in a distinct conformation compared to unsubstituted β-glucans. This represents a unique mode of xyloglucan recognition driven by α-linked side chain interactions rather than β-glucan backbone recognition alone. Together, these findings provide the first structural basis for xyloglucan oligosaccharide recognition by an ABC transporter in Gram-positive bacteria.
- Department of Chemical and Biological Engineering, Princeton University, NJ, USA.
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