NMR assignment and functional characterization of biotechnologically modified xanthan

Near-complete 1H/13C NMR chemical shift assignment of the xanthan repeating unit was achieved, unambiguously mapping beta-mannose and glucuronic acid resonances using multidimensional NMR plus engineered strains.

• Why it matters: Molecular-level structural characterization of xanthan is limited by high molecular weight, conformational rigidity, and severe NMR spectral overlap, especially for biotechnologically modified variants.
• What they did: The authors combined multidimensional NMR with targeted glycosyltransferase knockout strains (Delta gumI and Delta gumK) and controlled enzymatic depolymerization, then used temperature-dependent 1H NMR on variants lacking specific acetyl, pyruvyl, or sugar residues.
• The result: Side-chain composition is linked to thermal stability: removing pyruvate or negatively charged components increased order-disorder transition temperatures, while losing terminal beta-mannose destabilized the ordered conformation.

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