Expansins are secreted proteins of 25 to 27 Kd that were isolated first fromyoung cucumber seedling and subsequently from other plant tissues. Expressionof expansin genes correlates with growth of cells. Increase in expansincontent also occurs during fruit ripening. Expansins act on the cell wall topromote its extensibility. The model for its mechanism of action postulatesthat expansins break non-covalent bonds between cell-wall polysaccharides,thereby permitting pressure dependent expansion of the cell [1, 2].

Group-I pollen allergens of grasses have limited but significant sequencehomology to expansin. These proteins are the main causative agent of hay feverand seasonal asthma induced by grass pollen. Extracts containing group-Iallergens are also active in loosening cell-walls. Group-I pollen allergensand related proteins in vegetative tissues have been classified asbeta-expansins, whereas the earlier discovered expansins are now referred toas alpha-expansins [3].

Expansin-like proteins are also found in some fungi. In Trichoderma reesei anexpansin-like protein (Cel12A) acts as a glycoside hydrolase on xyloglucan and1-4 beta-glucan. These hydrolytic actions differ from the action by expansins,which induce wall extension by a non-hydrolytic mechanism [4].

Expansins consist of two domains closely packed and aligned so as to form along, shallow groove with potential to bind a glycan backbone of ~10 sugarresidues. The N-terminal cysteine-rich domain has distantsequence similarity to family-45 endoglucanases (EG45-like domain). The ~90-residue C-terminal domain may function as a cellulose-binding domain (CBD). Itis 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 [5].

This entry represents the expansin C-terminal CBD-like domain.

1. Loosening of plant cell walls by expansins. Nature 407, 321-6
2. Expansins: ever-expanding numbers and functions. Curr. Opin. Plant Biol. 4, 527-32
3. Group I allergens of grass pollen as cell wall-loosening agents. Proc. Natl. Acad. Sci. U.S.A. 94, 6559-64
4. A fungal endoglucanase with plant cell wall extension activity. Plant Physiol. 127, 324-33
5. Crystal structure and activities of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize. Proc. Natl. Acad. Sci. U.S.A. 103, 14664-71

Expansins are secreted proteins of 25 to 27 Kd that were isolated first fromyoung cucumber seedli
Show more...

Download genes (select columns to include)