Functional chondroitin sulfate from Enteroctopus dofleini containing a 3-O-sulfo glucuronic acid residue

•CS containing 13.9% of K-type units was found in Enteroctopus dofleini.•Population of fucosylated disaccharide units in octopus CS-K was low.•Octopus CS-K promoted neurite outgrowth activity in hippocampal neurons.•Octopus CS-K showed high affinity for growth factors. There are several reports that chondroitin sulfate containing K-type units [GlcA (3S)-GalNAc (4S)] exhibiting similar levels of neurite outgrowth promoting activities as CS having high amounts of B-, D- and E-type disulfated disaccharides. Although CS containing K-type units possess important biological activities, there are only few sources, such as king crab cartilage, squid cartilage or sea cucumber. In this study, CS containing 13.9% of K-type units was found in octopus (Enteroctopus dofleini) cartilage using different substrate specificities of chondroitinases. The 2D NMR spectra showed cross-peaks assigned to protons on sugar ring of GlcA (3S), demonstrating the presence of K-type units in octopus CS. Furthermore, proportion of fucosylated disaccharide units in octopus CS was very low. Octopus CS showed high affinity for growth factors and stimulated neurite outgrowth of hippocampal neurons, similar to the activity of squid CS-E. These results strongly suggest that octopus cartilage is a rich source of CS-K and has important biological activities.