Fig 5. Model for the role of the peptidoglycan framework in cellulose synthesis.

(A) The peptidoglycan framework providing guidance of glucan chains (green line) produced by each cellulose synthase complex located in the inner membrane through the periplasm to a pore, located in the outer membrane and in registry, to form a sub-elementary fiber for extrusion. Several sub-elementary fibers produced from more than one extrusion site aggregate to form a 3.5 nm elementary fibril, and adjacent elementary fibrils co-crystallize to form a 6–7 nm microfibril. (B) Effects of disruption of the peptidoglycan framework on assembly of glucan chains. The glucan chains (green line), synthesized in the inner membrane, may not be in perfect registry with the pore, and lack of guidance may result in some glucan chains not participating in the assembly of a sub-elemental fibril. Thus, the number of glucan chains that reach a pore may be reduced, and the less tightly packed glucan chains in the periplasm may allow non-cellulosic polysaccharides (purple curve line) to be incorporated into the sub-elementary fibril.