Xylan Decoration Patterns and the Plant Secondary Cell Wall Molecular Architecture

The molecular architecture of plant secondary cell walls is still not resolved. There are several proposed structures for cellulose fibrils, the main component of plant cell walls and the conformation of other molecules is even less well known. Glucuronic acid (GlcA) substitution of xylan (GUX) enzymes decorate the xylan backbone with various specific patterns of GlcA. Dicot xylan has a domain with the side chain decorations distributed on every second unit of the backbone (xylose).

If the xylan backbone folds in a similar way to glucan chains in cellulose (2-fold helix), this kind of arrangement may allow the undecorated side of the xylan chain to hydrogen bond with the hydrophilic surface of cellulose microfibrils. MD simulations suggest that such interactions are energetically stable. The possible role of this xylan decoration pattern in building of the plant cell wall is discussed.