| Type: | Domain | Name: | Expansin, cellulose-binding-like domain |
| Description: | Expansins are secreted proteins of 25 to 27 Kd that were isolated first from young cucumber seedling and subsequently from other plant tissues. Expressionof expansin genes correlates with growth of cells. Increase in expansin content also occurs during fruit ripening. Expansins act on the cell wall topromote its extensibility. The model for its mechanism of action postulates that expansins break non-covalent bonds between cell-wall polysaccharides,thereby permitting pressure dependent expansion of the cell [, ].Group-I pollen allergens of grasses have limited but significant sequence homology to expansin. These proteins are the main causative agent of hay feverand seasonal asthma induced by grass pollen. Extracts containing group-I allergens are also active in loosening cell-walls. Group-I pollen allergensand related proteins in vegetative tissues have been classified as beta-expansins, whereas the earlier discovered expansins are now referred toas alpha-expansins [].Expansin-like proteins are also found in some fungi. In Trichoderma reesei an expansin-like protein (Cel12A)acts as a glycoside hydrolase on xyloglucan and 1-4 beta-glucan. These hydrolytic actions differ from the action by expansins,which induce wall extension by a non-hydrolytic mechanism [].Expansins consist of two domains closely packed and aligned so as to form a long, shallow groove with potential to bind a glycan backbone of ~10 sugarresidues. The N-terminal cysteine-rich domain has distant sequence similarity to family-45 endoglucanases (EG45-like domain). The ~90-residue C-terminal domain may function as a cellulose-binding domain (CBD). It is composed of eight beta-strands assembled into two antiparallel beta-sheets.The two beta-sheets are at slight angles to each other and form a beta- sandwich similar to the Ig fold [].This entry represents the expansin C-terminal CBD-like domain. | Short Name: | Expansin_CBD |
