Morphology of Western larch arabinogalactan.

A molecular modeling study has revealed that (1 --> 3)-beta-D-galactan can not only adopt a triple helical structure similar to that of the corresponding glucan but can also accommodate a highly flexible beta-D-Gal-(1 --> 6)-beta-D-Gal disaccharide moiety as a side group 6-linked to every galactosyl unit in the main chain. The resulting triple helix, applicable to Western larch arabinogalactan, can assume quite different morphologies since the side group has access to several allowed conformational states. Some of the preferred modes of association between these helices have been visualized using preliminary X-ray fiber diffraction data.