A Molecular Description of Cellulose Biosynthesis

Abstract

Cellulose is the most abundant biopolymer on Earth, and certain organisms from bacteria to plants and animals synthesize cellulose as an extracellular polymer for various biological functions. Humans have used cellulose for millennia as a material and an energy source, and the advent of a lignocellulosic fuel industry will elevate it to the primary carbon source for the burgeoning renewable energy sector. Despite the biological and societal importance of cellulose, the molecular mechanism by which it is synthesized is now only beginning to emerge. On the basis of recent advances in structural and molecular biology on bacterial cellulose synthases, we review emerging concepts of how the enzymes polymerize glucose molecules, how the nascent polymer is transported across the plasma membrane, and how bacterial cellulose biosynthesis is regulated during biofilm formation. Additionally, we review evolutionary commonalities and differences between cellulose synthases that modulate the nature of the cellulose product formed.

A single heterologously expressed plant cellulose synthase isoform is sufficient for cellulose microfibril formation in vitro

“…However, the catalytic activity of Pichia-expressed PttCesA8 suggests that the enzyme either initiates cellulose biosynthesis in vivo using an expression host-provided factor [as observed for Rhodobacter BcsA upon expression in E. coli (14)] or that cellulose biosynthesis initiates in vitro upon incubation with UDP-Glc and Mn 2+ . Based on the Rhodobacter BcsA structure, priming of cellulose biosynthesis with monomeric glucose (derived from UDP-Glc hydrolysis) seems likely, as recently discussed (6,37).…”

“…CesA is an integral membrane protein predicted to contain an N-terminal cytosolic domain preceding two TM helices, an intracellular glycosyltransferase domain, and five C-terminal TM helices (6). If this prediction is correct, the odd number of TM helices would place the enzyme's N and C termini on opposing sides of the plasma membrane.…”

“…The mechanism by which CesA synthesizes and secretes individual glucan chains has been delineated recently for bacterial cellulose synthase (6)(7)(8); however, the process by which plant CesAs bundle these glucan chains into cellulose microfibrils is currently unknown. An intriguing hypothesis is that the oligomeric state of CesAs in the plasma membrane dictates the spontaneous association of the extruded glucan chains into microfibrils (9,10).…”

Mechanism of a cytosolic O -glycosyltransferase essential for the synthesis of a bacterial adhesion protein

“…Our results show that GtfA/B is a nonprocessive enzyme. This mechanism is in contrast to polysaccharide-synthesizing enzymes, such as cellulose synthase (41). In this case, there is directed synthesis through the membrane, which prevents the release of the growing substrate into the cytosol.…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…Cellulose microfibrils are aggregates of linear b-1,4-linked glucan chains, which are stabilized by intramolecular and intermolecular hydrogen bonds in the walls (Notley et al, 2004;McNamara et al, 2015). Several types of methods have been used to visualize the microfibrils in the wall (Table I).…”