Immunologically active O6-branched (1-->3)-beta-glucan from the lichen Thamnolia vermicularis var. subuliformis

A lentinan-type gel-forming beta-glucan, Ths-2, has been isolated in about 1.5% yield from the alkali extract of the lichen Thamnolia vermicularis var. subuliformis, using ethanol fractionation, dialysis and gel filtration. The mean Mr of Ths-2 was determined by GP-HPLC to be 67 kD, and the optical rotation was measured to be -14 degrees. The structure of Ths-2 was further elucidated by methylation analysis by GC-MS, 1H- and 13C-NMR spectroscopy and selective enzymatic hydrolysis with exo-(1 --> 3)-beta-D-glucanase followed by analysis of oligosaccharides by HPAEC-PAD. Ths-2 was found to be consisting of a (1 --> 3)-beta-D-glucopyranosyl main chain with branches of a (1 --> 6) linked glucopyranosyl unit on every third unit of the main chain. Similar polysaccharide structures have been described from fungi, but this is the first report of a lentinan-type (1 --> 3)-beta-D-glucan from a lichen species. The immunomodulating activity of Ths-2 was tested in an in vitro anti-complementary assay, and proved to be strongly active.