Dermatan sulfate and chondroitin 6-sulfate conformations

X-ray diffraction patterns show that dermatan sulfate in oriented, crystalline films occurs as two or three or eight-fold helices. The two-fold helix has a greater axial rise per disaccharide residue [ h = 9.6 A ̊ ] than the corresponding chondroitin 6-sulfate helix [ h = 9.3 A ̊ ] . Three-fold dermatan sulfate and chondroitin 6-sulfate helices both have h = 9.5 A ̊ . Consequently the α-L-iduronate residues in dermatan sulfate helices have the C1 chair conformation like β-D-glucuronate in chondroitin 6-sulfate. Since the eight-fold dermatan sulfate helix has h = 9.3 A ̊ rather less than the eight-fold chondroitin 6-sulfate helix [ h = 9.8 A ̊ ] the possibility of α-L-iduronate 1C chairs cannot be ruled out for it. Computer methods have been used to produce molecular models. In these the polysaccharide chains are almost linear. Each backbone conformation can accommodate a variety of arrangements of charged side groups.