Expansin are proteins that induced plant cell wall loosening, but their exact target and mechanism of action remain elusive. No enzymatic activity has been verified for any expansin and plant expansins have proved difficult to express in an active form in heterologous systems. We conducted a structure-function analysis of the recently discovered Bacillus subtilis expansin EXLX1 which consists of domains D1 and D2. Residues forming the hydrophobic surface on domain D2 and its extension in domain D1  are important for wall loosening and paper weakening activity. Domain D2 mediates EXLX1 binding to cellulose through aromatic amino acids and to negatively charged matrix polysaccharides through positively charged amino acids.  Binding to cellulose is linked to wall loosening and cellulose weakening activity. Wall loosening by EXLX1 most likely takes place on crystalline cellulose or the interface between crystalline and amorphous cellulose.

Structure-function analysis of plant cell wall binding and loosening by a bacterial expansin

243rd National Meeting (2012)

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