9PMY

Crystal Structure of an ATP-Binding Cassette (ABC) Transporter Associated, Xyloglucan-Binding Protein from the Extremely Thermophilic, Lignocellulose Degrading Bacterium Anaerocellum (f. Caldicellulosiruptor) bescii

Summary for 9PMY

• Entry DOI: 10.2210/pdb9pmy/pdb
• Descriptor: Extracellular solute-binding protein family 1, PHOSPHATE ION (3 entities in total)
• Functional Keywords: sugar binding protein, xyloglucan, abc substrate binding, thermophile
• Biological source: Caldicellulosiruptor bescii
• Total number of polymer chains: 2
• Total formula weight: 126283.91

Authors

Tjo, H.,Jeffrey, P.D.,Conway, J.M. (deposition date: 2025-07-18, release date: 2026-07-29, Last modification date: 2026-08-26)

Primary citation

Tjo, H.,Jiang, V.,Jeffrey, P.D.,Zhu, A.,Link, A.J.,Joseph, J.A.,Conway, J.M.
Structural insights into xyloglucan recognition by an ABC transporter from a Gram-positive, thermophilic bacterium.
Febs J., 2026

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 = 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.

PubMed: 42545829
DOI: 10.1111/febs.70667

Experimental method

X-RAY DIFFRACTION (2.43 Å)