## 11 Multifunctionality of the Newly Characterized Processive Endocellases
Moreover, the lack of GH5-p4818 Cel5_2A activity on the purified arab binoculars would indicate that this branched structure polymer substrate could not be acted on by this enzyme, while the lack of GH5-p4818 Cel5_2A activity on the purified arabian from this study would also suggest that GH5-p4818 Cel5_2A had no arabian endo-(1,5)-\(\alpha\)-L-arabininase activity (EC 3.2.1.99) and no \(\alpha\)-L-arabinofuranosidase activity (EC 3.2.1.55) [45]. Some GH5 endocelllases with dual substrate specificity such as concurrent activities on glucan-mann or glucan-xylan have been well documented [159; 165]. [PERSON] et al. [166] reported that the hyperthermophilic _Thermotoga maritima_ GH5 endoglucanase Cel5A had activities on soluble CMC, barley \(\beta\)-glucan, xyloglucan, lichen, galatomanan and glucomanan; however, it had no activities on important plant cell wall substrates of crystalline celluloses and xylan. [PERSON] et al. [167] suggested that the GH5 multifunctional properties likely descended from an ancestral enzyme gene through bioinformatic phylogenetic analyses. [PERSON] et al. [118] and [PERSON] et al. [69] reported that GH5 procesive endoglucanase Cel5A in the brown rot basidomycete _Postia placenta_ and the ruminal _Fibrobacter succinogenes_ GH9D had concurrent activities on crystalline cellulose and xylan. The bi-modular endo-acting and exo-acting processive and bi-functional thermophilic _Caldicellulosiruptor besci_ endocellase CelA were shown to hydrolyze both crystalline cellulose and xylan [103], which feature was highly regarded as an outstanding potential industrial cellulase for saccharification without required physicochemical pretreatment of feedstock [77; 88]. However, the _Clostridium thermocellum_ noncellulosomal GH9, the _Clostridium Phytrofermentans_ GH9 and the _Saccharophag degradans_ GH5 processive endoglucanases were all characterized to only hydrolyze cellulose substrates [78; 131; 133]. The current commercial cellulase enzyme products that are primarily derived from the aerobic fungal species of _Trichoderma reseei_, _Humicola insolens_, _Aspergillus niger_ and basidomycete _Ipex lactaeus_ do not possess hydrolytic properties beyond crystalline celluloses, CMC, barley glucans and/or xylan. To the best of our knowledge, the GH5-CelSA1 variants and particularly GH5-p4818 Cel5_2A have been the only processive endocellase characterized so far to have multiple substrate specificity in hydrolyzing multiple plant cell wall substrates including crystalline cellulose, pretreated cellulose and \(\beta\)-glucan, as well as hemicellulose of xylan, xyloglucan, glucomannan and galactomannan. Under this context, it is known that hemicellulosees are important components of plant cell wall materials embedding elemental fibril crystalline cellulose core for each of microfibrillar units, reducing porosity, and hampering cellulases from further penetration into microfibrillar internal surfaces for effective hydrolysis. Physicochemical pretreatment of plant cell wall biomass materials for removal of hemicellulose accounts for up to 22% of the total projected cost of producing commercial scale of lignocellulosic ethanol [24]. [PERSON] et al. [168] reviewed that the current trend in the developing second-generation lignocellulosic and hemicellulose ethanol industry is to use of pretreatment of lower severity by combining biochemical conversion technology in order to lower the capital cost and also to minimize waste generation. For example, the first commercial scale second-generation fuel ethanol plant, Beta Renewables plant in Crescentino, Italy, utilizes only steam in its pretreatment without chemical addition [168]. Uses of hemicellulases following this steam pretreatment would further increase porosity, constituent soluble sugar yields and fluidity of the pretreated feedstock slurry, since \(\beta\)-glucans, xyloglucans, xylan and arabinoxylans are very viscous [168]. [PERSON] et al.