Structure identification and biological activity of a novel sulfated glycosaminoglycan-like polysaccharide from Sepia recurvirostra ink

A novel sulfated glycosaminoglycan-like polysaccharide (SIP), with a molecular weight of 13.78 kDa, was isolated from Sepia recurvirostra ink. SIP displayed a sulfate content of 6.82 % and consisted of GlcNAc, GalNAc, GlcA and Fuc. The distinct structural sequence of SIP was identified by 1D/2D NMR assignments of the backbone released by deaminative treatment and the oligosaccharides generated by mild acid hydrolysis. The backbone was built up of disaccharide repeating blocks structured as [−D-GlcA-β1,4-L-Fuc-α1,3-]. Notably, the non-sulfated GalNAc was attached to C-3 of Fuc, while the 4, 6-O-disulfated GlcNAc was pendant at C-4 in 20 % of GlcA residues, as revealed by the well-defined structures of trisaccharide, tetrasaccharides, heptasaccharides and decasaccharides. Except for the trisaccharide, the non-reducing ends of the other oligosaccharides were GlcNAc 6 S or GlcNAc 4S6S , suggesting selectivity of glycosidic bond cleavage and desulfation during mild acid hydrolysis. SIP showed negligible anticoagulant and heparanase inhibitory activity. Moreover, the effects of SIP on the generation of short-chain fatty acids (SCFAs) by colonic microbiota were evaluated. The addition of SIP resulted in a significant increase in levels of acetate, propionate, isobutyric acid, and isovaleric acid, offering insights into the contribution of the colonic microbiota to the health benefits of dietary squid ink.