About Expansins...
Home About Expansins... Protein Structure Expansin Genes abstracts Nomenclature

Expansins are plant cell wall proteins first discovered in studies of plant cell enlargement. They have unique "loosening" effects on plant cell walls and are thought to function in plant cell growth, cell wall disassembly, cell separation, pollen tube penetration (in grasses, at least) and leaf primordium initiation. The first studies of expansin proteins, their genes, and their action on cell walls began in the Cosgrove lab, but other groups are now adding new insights about expansins. 

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ACTIVITY:  Two related actions are characteristic and diagnostic for expansins: 

  1. They induce long-term, irreversible extension (creep) of plant cell walls.
                            (More about wall creep)
  2. They enhance stress relaxation of walls over a wide time range (<0.1 to >100 s). 
                            (More about wall stress relaxation)

Both of these actions are pH dependent, with an acidic optimum. No enzymatic activity has been detected with expansins and their mechanism of action remains enigmatic.

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 PROTEINS:  Two classes of expansin proteins are currently recognized, called alpha-expansins and beta-expansins.

bulletAlpha-expansins are a highly conserved group of proteins hypothesized to control cell wall enlargement and perhaps other developmental processes including cell wall disassembly and cell separation.
bulletThe first beta-expansins to be discovered were previously known as group-1 grass pollen allergens. They are profusely secreted by grass pollen and have potent wall loosening effects on grass cell walls. Their biological function seems to be to soften the stigma and stylar tissues to speed penetration of the pollen tubes through the maternal tissues to the ovule. The presence of many other beta-expansins in young grass seedlings and non-pollen tissues hints that this expansin class has a variety of developmental functions related to their wall-loosening action.
bulletMany expansin cDNAs and genes have been identified in plants

This page was last updated on 03/22/06.

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