Synthetic carbohydrate-binding module-endogalacturonase chimeras increase catalytic efficiency and saccharification of lignocellulose residues.

Primary cell walls and middle lamella of higher plants include homogalacturonan, the substrate for polygalacturonases. Seeking to enhance lignocellulose saccharification, chimeras between the endopolygalacturonase I from Chondrostereum (Stereum) purpureum (EndoPG-I) and family 3, 44, and 77 carbohydrate-binding modules (CBMs) from Hungateiclostridium thermocellum (Ht) or Ruminococcus flavefaciens (Rf) were constructed, expressed, and characterized. Chimeras presented similar K_M values and pH/temperature optima as unfused EndoPG-I against citrus pectin, k_cat/K_M values 1.6, 1.7, and 1.3-fold higher for the HtCBM3-EndoPG, HtCBM44-EndoPG, and RtCBM77-EndoPG, respectively. Commercial enzyme cocktail supplementation with HtCBM44-EndoPG and RtCBM77-EndoPG increased reducing sugar release from untreated sugarcane bagasse by 35 and 25%, respectively. All chimeras increased reducing sugar release by 20–25% against orange bagasse compared with EndoPG-I or equimolar EndoPG-I/CBM mixtures. These results show that proximity between plant cell wall components in situ influences CBM-enzyme chimera activity and improves saccharification of lignocellulosic materials. [ABSTRACT FROM AUTHOR]