Cellulose structure and biosynthesis *

Carbohydrate researchers may think it is reasonable to believe that the synthesis and structure of a crystalline b-1,4 glucan would be quite straightforward; however, this is not the case. The pitfalls and detours of research have been counterbalanced by exciting new discoveries in cellulose structure, biosynthesis, and molecular biology. Cellulose exists in crystalline and noncrystalline states, with the metastable cellulose I allomorph being the most abundant native crystalline form. Two stages of cellulose I crystallization will be described as well as a new form of ordered, noncrystalline cellulose known as quasi-tactic cellulose. The biosynthesis of cellulose is exceedingly complex, involving many genes and enzymes. Ordered membrane complexes (TCs) control the polymerization and crystallization to form cellulose micro®brils. Biochemical investigations have proven to be very dif®cult; however, recent breakthroughs on in vitro cellulose I assembly lend con®dence that this part of cellulose research will soon yield great advances. The greatest success has come from molecular genetics research where the genes for cellulose biosynthesis from Acetobacter have been identi®ed, cloned, mutated, and expressed in other systems. The multidomain architecture of b-glycosyl transferases has led to a better understanding of glucan chain polymerization leading to the twofold screw axis in cellulose as well as ®nding similar domains hypothesized to function in higher plant cellulose biosynthesis. The recent ̄urry of activity in this ®eld promises to give even more clues to the developmental regulation of cellulose biosynthesis among plants, including the major textile and forest crops.