A Fucan Sulfate with Pentasaccharide Repeating Units from the Sea Cucumber Holothuria floridana and Its Anticoagulant Activity

A fucan sulfate (HfFS) was isolated from the sea cucumber Holothuria floridana after proteolysis-alkaline treatment and purified with anion-exchange chromatography. The molecular weight (Mw) of HfFS was determined to be 443.4 kDa, and the sulfate content of HfFS was 30.4%. The structural analysis of the peroxidative depolymerized product (dHfFS-1) showed that the primary structure of HfFS was mainly composed of a distinct pentasaccharide repeating unit -[L-Fuc(2S4S)-alpha(1,3)-L-Fuc-alpha(1,3)-Fuc-alpha(1,3)-L-Fuc(2S)-alpha(1,3)-L-Fuc(2S)-alpha(1,3)-](n)-. Then, the "bottom-up" strategy was employed to confirm the structure of HfFS, and a series of fucooligosaccharides (disaccharides, trisaccharides, and tetrasaccharides) were purified from the mild acid-hydrolyzed HfFS. The structures identified through 1D/2D NMR spectra showed that these fucooligosaccharides could be derivates from the pentasaccharide units, while the irregular sulfate substituent also exists in the units. Anticoagulant activity assays of native HfFS and its depolymerized products (dHf-1 similar to dHf-6) in vitro suggested that HfFS exhibits potent APTT-prolonging activity and the potencies decreased with the reduction in molecular weights, and HfFS fragments (dHf-4 similar to dHf-6) with Mw less than 11.5 kDa showed no significant anticoagulant effect. Overall, our study enriched the knowledge about the structural diversity of FSs in different sea cucumber species and their biological activities.