Structural analysis and anti-complement activity of polysaccharides extracted from Grateloupia livida (Harv.) Yamada

Abstract

Polysaccharides were extracted from Grateloupia livida (Harv.) Yamada using hot water (extracted product denoted WGW) and then degraded in dilute sulfuric acid (degraded product denoted WGWD). The degraded mixture was then separated into four fractions through anion exchange chromatography on 2-diethylaminoethanol (DEAE)-Bio-Gel Agarose FF gel. Electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) was performed to elucidate the structural features of all fractions. In combination with nuclear magnetic resonance spectroscopy (NMR) and infrared spectroscopy (IR) data, the major polysaccharide structures were concluded to be µ-carrageenan and κ-carrageenan. µ-Carrageenan usually has a backbone of alternating 1,3-linked s-D-galactopyranose residues sulfated at C-4 and 1-4-linked α-D-galactopyranose residues sulfated at C-6, while κ-carrageenan consists of alternating 1,3-linked s-D-galactopyranose residues sulfated at C-4 and 1,4-linked α-D-3,6-anhydrogalactopyranose residues. Trace v-carrageenan- composed of 1,3-linked s-D-galactopyranose residues sulfated at C-4 and 1,4-linked α-D-galactopyranose residues sulfated at C-2 and C-6, was also detected. Furthermore, the polysaccharide had a backbone comprising 1,3-linked s-D-galactopyranose and 1,4-linked α-L-galactopyranose sulfated at C-6, which is the agarose precursor. The hydroxy groups in the galactopyranose were partially substituted by methyl and pyruvic acid acetal (PA) groups. The anti-complementary activities of WGW and its derivatives against classical pathways were measured. The native polysaccharides in WGW had higher activities, while the derivatives had much weaker activities. This indicated that the molecular weight and sulfate content were important factors affecting the anti-complement activity.