## 11 Multifunctionality of the Newly Characterized Processive Endocellases  
The enzyme activity results summarized in Table 1 have shown that apart from hydrolysis on crystalline, amorphous and soluble celluloses, tCel5A1 and the GH5-p4818_2A could effectively hydrolyze four other hemicelluloses & hemicellulose complex substrates. The GH5-p4818 Cel5_2A activity in hydrolyzing xyloglucans was 57%, much higher than its endocellase activity in hydrolyzing Avicel has important industrial applications [45]. Firstly, as one of the main branched structural and principal storage hemicellulose polysaccharides, xyloglucans are present in all land plants and comprise between 20 and 50% of the plant cell wall or seed dry mass [162]. Secondly, xyloglucans are \(\beta\)-(1,4)-linked D-glucosebackbone heavily substituted with \(\alpha\)-(1,6)-xylose-linked side-chain polymers. Xyloglucans are not linear polymers but branched-structure polymers. Xyloglucan-specific hydrolytic activites are carried out by three enzyme activities of xyloglucan-specific \(\beta\)-(1,4)-endoc-xyloglucanase activity (EC 3.2.1.151). \(\beta\)-(1,4)-exo-xyloglucanase activity (EC 3.2.1.155) and oligoxyoglucan reducing-end-specific cellobiohydrolase activity (EC 3.2.150) [162]. The GH5-p4818 Cel5_2A activity on xyloglucans by measuring reducing sugar yield would at least suggest that this endocelllase has significant EC 3.2.1.151 activity. Further studies are needed to determine the hydrolytic end-products of the tCel5A1 and GH5-p4818 Cel5_2A activity on xyloglucans and to further characterize if this endocelllase also possesses the exo-acting mode of EC 3.2.1.155 and EC 3.2.150 activities by following the procedures of [PERSON] et al. [162]. Xyloglucan-specific hydrolytic activities have been demonstrated in several members of GH families including GH5, 7, 9, 12, 44 and 74 [162]. [PERSON] et al. [163] demonstrated that _Trichoderma_ viride but not _Trichoderma_ _resei_ cellulases had hydrolytic activities towards Xyloglucans. The previously reported xyloglucan-specific hydrolytic activities in two GH5 enzymes were a GH5_4 subfamily with xyloglucan-specific \(\beta\)-(1,4)-endo-xyloglucanase activity (EC 3.2.1.151), and/or \(\beta\)-(1,4)-exo-xyloglucanase activity (EC 3.2.1.155) with the enzyme genes being cloned and characterized from _Paenibacillus sp._[159; 164]. These _Paenibacillus sp._ GH5 xyloglucanases were only active towards xyloglucans and not towards Avicel, CMC, barley glucan or xylan [160]. However, Cel5A1 and variants did not show detectable xyloglucan-specific hydrolytic activity [137]. Thus, GH5-p4818 Cel5_2A is likely among the first reported multifunctional monomodular processing endcelllases being associated with xyloglucan-specific hydrolytic activity. Furthermore, GH5-p4818 Cel5_2A activities on the purified birch wood xylan as well as Kojac glucomanan and locust bean gum, i.e., galactomannan that was also a branched structure polymer, whereas GH5-Cel5A1 variants had activities on Kojac glucomanan and locust bean gum, i.e., galactomannan; these findings would suggest that the GH5-p4818 Cel5_2A endocelllase have the \(\beta\)-(1,4)-endo-xylanase activity (EC 3.2.1.21) and the \(\beta\)-(1,4)-endo-mannanase activity (EC 3.2.1.78) [45], and GH5-Cel5A1 variants have the \(\beta\)-(1,4)-endo-mannanase activity [137]. Given the fact that both GH5-Cel5A1 variants and GH5-p4818 Cel5_2A also have exo-acting activity, further measurements need to be conducted to examine if GH5-p4818 Cel5_2A has xylan \(\beta\)-(1,4)-xylosidase activity (EC 3.2.1.37) and \(\beta\)-(1,4)-mannosidase activity (EC 3.2.1.25) and if GH5-Cel5A1 variants also have \(\beta\)-(1,4)-mannosidase activity. On the other hand, the lack of activity by GH5-Cel5A1 variants and GH5-p4818 Cel5_2A on colloidal chitin would suggest that these endocelllase had no chitosan native activity (EC 3.2.1.149) [45; 137].