The carbohydrate-binding module of Fragaria × ananassa expansin 2 (CBM-FaExp2) binds to cell wall polysaccharides and decreases cell wall enzyme activities “in vitro”
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A putative carbohydrate binding module (CBM) from strawberry (Fragaria × ananassa Duch.) expansin 2 (CBM-FaExp2) was cloned and the encoding protein was over-expressed in Escherichia coli and purified in order to evaluate its capacity to bind different cell wall polysaccharides “in vitro”. The protein CBM-FaExp2 bound to microcrystalline cellulose, xylan and pectin with different affinities (Kad = 33.6 ± 0.44 mL g−1, Kad = 11.37 ± 0.87 mL g−1, Kad = 10.4 ± 0.19 mL g−1, respectively). According to “in vitro” enzyme assays, this CBM is able to decrease the activity of cell wall degrading enzymes such as polygalacturonase, endo-glucanase, pectinase and xylanase, probably because the binding of CBM-FaExp2 to the different substrates interferes with enzyme activity. The results suggest that expansins would bind not only cellulose but also a wide range of cell wall polymers.
KeywordsCBM Cell wall Expansin Hydrolases Strawberry
This work has been supported by grants from CONICET (PIP 0062), ANPCYT (PICT 2006-01140) and UNSAM (Biotechnology Program 2007). Authors thank José Luis Burgos (Comisión de Investigaciones Científicas, CIC) for valuable technical assistance.
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