Figure 1. Model reaction sequence for cellulose synthesis by A. tumefaciens.

Figure 2. Diagrammatic representation of cellulose synthase (CesA) proteins in the plasma membrane of an embryophyte cell and their interaction through a zinc-finger domain. The zinc-finger domain at the N-terminus of CesA proteins can exist in either a reduced or oxidized form. Under reduced conditions, this domain coordinates two zinc ions and can interact with either lipid transfer protein (LTP), metallothionein (Mt), microtubules (MT) or cysteine protease. Under oxidized conditions, the CesA protein can dimerize with itself or another CesA protein. Proteins such as the Korrigan endocellulase (Kor), the plasma membrane-associated form of sucrose synthase (pm-SuSy), actin and the herbicide CGA binding protein (CGAbp), all of which have been implicated in cellulose synthesis, are shown. Reproduced from Doblin et al. (2002).

Figure 3. Possible catalytic mechanism for an inverting, NDP-dependent glycosyl transferase. The leaving group (^–O-NDP) departure is assisted by an aspartate residue in the catalytic site (not shown). A second aspartate acts as the general base, by abstracting a proton from the terminal glycosyl residue of the nascent polysaccharide chain (H–O–R). Reproduced from Charnock and Davies 1999.

Figure 4. Domain structures of CesA related proteins showing regions homologous in prokaryote and eukaryote cellulose synthase proteins with their conserved aspartate and QXXRW motifs. The embryophyte-specific and conserved domains and the embryophyte hypervariable regions are shown. Reproduced from Delmer (2000).

Figure 5. Freeze-etch replica of fractured bacterial lipopolysaccharide surface region of Gluconoacetobacter xylinus showing a region of overlap of two separate rows of synthesizing sites. Reproduced from Haigler and Benziman (1982).

Figure 6. Freeze-fracture images of rosettes of terminal complexes (diameter nm) in the P-fracture face of a plasma membrane from the first internode of barley (Hordeum vulgare L. cv. Kobinkatagi). Reproduced from Kimura et al. 1999.

Figure 7. (a) Schematic representation of Trichoderma reesei cellobiohydrolase 1(CBH1) catalytic domain with a cello-nonosaccharide (reducing end on the right) bound in the tunnel-shaped active site. The catalytic pair of glutamic acid residues (not shown) lie above and below the site of chain cleavage of the substrate chain between the second and third residues from the reducing end. The secondary-structure elements are coloured as follows: strands, blue arrows; helices, red spirals; loop regions, yellow coils. The cello-oligosaccharide is shown in pink as the ball-and-stick object. Reproduced from Divne et al. (1998). (b) Model of intact cellobiohydrolase 1 (CBH1) from Trichoderma reesei bound to a cellulose microfibril surface. The model is based on the crystal structure of CBH1 in complex with cellohexaose, the NMR structure of the cellulose binding domain (CBD) and a modelled linker region. CBH1 is believed to act repetitively from the reducing end towards the nonreducing end of the cellulose chain. Reproduced from Munoz et al. (1999).

Figure 8. (a) Schematic representation of cellulosome organization and attachment to the surface of Clostridium thermocellum. The cellulosome and its associated anchoring proteins all comprise modular components. The scaffoldin protein shown in yellow, is composed of nine copies of a cohesin module, a CBD and a dockerin domain. The cellulose-binding, planar aromatic strip of the CBD, and the putative dockerin-binding residues of the cohesin are highlighted in red. The schematic cellulosomal catalytic units shown in shades of blue, green and purple, represent five different classes of catalytic subunits found in cellulosomal subunits. The enzymes are shown bound to the scaffoldin protein via their attached and highly conserved, dockerin domains. The entire cellulosome, comprising scaffoldin proteins and the catalytic subunits, is bound to the cell surface (left) in either single or multiple copies by interaction with resident type-II dockerin with type II cohesin domains of cell surface anchoring proteins, shown in orange. (b) Diagrammatic representation of a Clostridium thermocellum cell bound to cellulose. The cellulosome protuberances on the cell surfaces are shown in their resting state and in their extended state upon binding to the substrate. Reproduced from Bayer et al. (1998).