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Xanthomonas campestris expansin-like X domain is a structurally disordered beta-sheet macromolecule capable of synergistically enhancing enzymatic efficiency of cellulose hydrolysis

Junior, Atílio Tomazini, Dolce, Luciano Graciani, de Oliveira Neto, Mario, Polikarpov, Igor
Biotechnology letters 2015 v.37 no.12 pp. 2419-2426
Bacillus subtilis, X-radiation, Xanthomonas campestris, cellulases, cellulose, circular dichroism spectroscopy, culture media, depolymerization, gel chromatography, hydrolysis, ion exchange, pH, rendering, sugars, synergism
OBJECTIVES: To biochemically characterize an expansin-like X protein domain from Xanthomonas campestris (XcEXLX1) and to study its synergy with cellulases in cellulose depolymerization. RESULTS: The protein was purified using a combination of ion exchange and size exclusion chromatography rendering about 30 mg pure protein/l culture medium. Circular dichroism spectroscopy and small-angle X-ray scattering studies of XcEXLX1 reveal that it is a strongly disordered β-sheet protein. Its low resolution envelope fits nicely the crystallographic structure of the homologous protein EXLX1 from Bacillus subtillis. Furthermore, we demonstrate that XcEXLX1 shows a synergistic, pH-dependent effect when combined with a commercial enzymatic preparation (Accellerase 1500), enhancing its hydrolytic activity on a cellulosic substrate. The strongest effect was observed in acid pHs with an increase in sugar release of up to 36 %. CONCLUSION: The synergistic effect arising from the action of the expansin-like protein was considerable in the presence of significantly larger amounts of the commercial enzymatic cocktail then previously observed (0.35 FPU of Accellerase 1500/g substrate).