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 GlcNAc6S or GlcNAc4S6S, 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.