Refinement and complete solution NMR analysis of the structure of a 6-branched 1,3-β-D-glucan (OL-2) isolate from Omphalialapidescens.

OL-2 is a water-soluble β-glucan produced by Omphalia lapidescens. This versatile glucan has potential applications in various industries, including food, cosmetics, and pharmaceuticals. In addition, OL-2 is known for its promising applications as a biomaterial and drug, owing to its reported antitumor and antiseptic properties. Although the biological activities of β-glucans vary depending on their primary structure, holistic clarification of OL-2 via solution NMR spectroscopy to ascertain its complete and unambiguous structure has not yet been achieved. In this study, a chain of solution NMR techniques, such as correlation spectroscopy, total correlation spectroscopy (TOCSY), nuclear Overhauser effect and exchange spectroscopy, C-edited heteronuclear single quantum coherence (HSQC), HSQC-TOCSY, heteronuclear multiple bond correlation, and heteronuclear 2-bond correlation pulse sequences were used to unambiguously assign all H and C atoms in OL-2. Based on our investigation, OL-2 consists of a 1,3-β-glucan backbone chain decorated with a single 6-branched β-glucosyl side unit on every fourth residue.