Expansins

Biochemical dissection of the "acid growth" process of plant cell walls led to the isolation of a new class of wall loosening proteins, called expansins. These proteins affect the rheology of growing walls by permitting the microfibril-matrix network to slide, thereby enabling the wall to expand. Molecular sequence analysis suggests that expansins might have a cryptic glycosyl transferase activity, but biochemical results suggest that expansins disrupt noncovalent bonding between microfibrils and the matrix. Recent discoveries of a new expansin family and gene expression in fruit, meristems and cotton fibers have enlarged our view of the developmental functions of this group of wall loosening proteins.