Structural characterization of ulvan extracted from Ulva clathrata assisted by an ulvan lyase

Rhamnan-rich sulfated polysaccharides extracted from green algae (ulvan) constitute potentially useful natural materials for drug development. However, the characterization of their complex structures poses a challenge for their application. In this study, the structure of ulvan extracted from Ulva clathrata was analyzed with the assistance of an ulvan lyase belonging to the PL25 family. According to mass spectrometry and nuclear magnetic resonance analysis of the degraded oligosaccharides, the backbone of such a polysaccharide mainly consisted of -> 4)-beta-D-GlcA-(1 -> 4)-alpha-L-Rha3S-(1 -> and -> 4)-beta-D-Xyl-(1 -> 4)-alpha-L-Rha3S-(1 -> disaccharide repeating units, and the ratio is approximately 4:1. In addition, about 4% of the xylose moieties bear sulfate groups. Minor amounts of branches containing hexose and unsaturated glucuronic acid were found during the sequence analysis of hexa- to octasaccharides. These results indicated the presence of a long branch in the ulvan. The clarification of the detailed structure provides a foundation for ulvan modification and its structure-activity relationship studies.