Polysaccharides from Codium species: chemical structure and biological activity. Their role as components of the cell wall

Abstract

Polysaccharides from Codium species have drawn attention due to their high anticoagulant activity. However, many different mechanisms of action have been proposed and the structure of the active compounds was usually not elucidated. Recently, structural determination has been carried out using purified fractions showing the presence of at least three different polysaccharide types, namely: (1) 3-linked B-D-galactans with ramifications on C-6 and terminal B-D-galactopyranose units with pyruvic acid ketal linked to O-3 and O-4 (S-configuration). Sulphation occurs mainly on C-4 and some of the 3-linked galactose units are substituted by pyruvic acid ketals linked to O-4 and O-6 (R-isomer). (2) 3-linked linear pyranosic B-L-arabinans sulphated on C-2 and/or C-4. (3) 4-linked B-D-mannans, partially sulphated on C-2 or on C-6, but to a lesser extent. The backbone of this polysaccharide is similar to that of the fibrillar component of the cell wall. Antiherpetic activity and activity on the immune system were determined for sulphated galactans from Codium fragile, which do not have significant anticoagulant effect, while highly sulphated arabinans have an important anticoagulant activity by mechanisms different to those described for heparin. The utricle cell wall of C. fragile has a sandwich structure of two fibrillar-like layers delimiting a middle amorphouslike zone. Mannans and hydroxyproline-rich glycoprotein-like epitopes are located in two distinct cell-wall layers, whereas sulphated polysaccharides are distributed in the middle area of the wall. The overall cell-wall polymer arrangement in the utricles of different species proved to be somewhat different.