Structural characterization of a cell wall-associated polysaccharide of Nocardia rubra FIM-21 and its immunostimulatory activity

In this work, a neutral polysaccharide named NP-1 was obtained from the cell wall of Nocardia rubra FIM-21 by column chromatography. Its chemical structure was characterized by methylation analysis, 2D NMR spectroscopic study, and other techniques. It was shown that NP-1 contained five types of monosacchrides, including mannose (Man), glucose (Glc), N-acetylglucosamine (GlcpNAc), galactose (Gal) and arabinose (Ara) in a molar ratio of 7.7:3:2:1:1.5. According to linkage analysis and NMR spectra, the backbone contains 1,6-linked Manp, 1,4-linked Glcp, and 1,6-linked Galp, with branches substituted at the C-6 of 1,4-linked Glcp and the C-2 of 1,6-linked Galp by GlcpNAc, and at C-2 of 1,6-linked Manp by Araf, Araf-1,5-Araf or GlcpNAc. Biological activity research showed that NP-1 could stimulate the proliferation of RAW264.7 cells and enhance their phagocytosis and release of NO.