Membrane pore architecture of the CslF6 protein controls (1-3,1-4)-b-glucan structure

The cereal cell wall polysaccharide (1-3,1-4)-b-glucan is a linear polymer of glucose containing both b1-3 and b1-4 bonds. The structure of (1-3,1-4)-b-glucan varies between different cereals and during plant growth and development, but little is known about how this is controlled. The cellulose synthase–like CslF6 protein is an integral membrane protein and a major component of the (1-3,1-4)-b-glucan synthase. I show that a single amino acid within the predicted transmembrane pore domain of CslF6 controls (1-3,1-4)-b-glucan structure. A new mechanism for the control of the polysaccharide structure is proposed where membrane pore architecture and the translocation of the growing polysaccharide across the membrane control how the acceptor glucan is coordinated at the active site and thus the proportion of b1-3 and b1-4 bonds within the polysaccharide.