## 11 Multifunctionality of the Newly Characterized Processive Endocellases
[181] shown that several fungal cellulases were resistant to proteolytic activities that were of bovine ruminal microbial origins and addition of non-enzyme sources of proteins could further dilute the ruminal proteolytic effects on the fungal endocellular activities. [PERSON] et al. [182] reported a novel GH9 beta-glucanase that was cloned and characterized from thermoacidophilic _Alicyclobacillus sp_. and was highly resistant to various proteases when this enzyme was expressed in the yeast _Pichia pastoris_ likely in a glycosylated form. [PERSON] et al. [55] reported that a novel GH5 cellulase from buffalo rumen metagenome was highly resistant to proteases. [PERSON] et al. [177] viewed that \(O\)-glycosylation imparts protease resistance for the fact that glycans presumably block proteases access to the protein backbone. However, pepsin is an important animal gastric protease and its effects on cellulase activities are not well reported in the literature. [PERSON] et al. [183] reported that porcine gastric pepsin activity ranged from 143 to 266 PU (pepsin activity unit)/mL digest fluid. Further efforts should be made to examine effects of pepsin, trypsin and chymotrypsin activities on both GH5-tCel5A1 and GH5-p4818 Cel5_2A endocellular activity in the presence feed proteins under close to normal physiological conditions such as at the porcine physiological body temperature of 37 \({}^{\circ}\)C, a typical gastric pH for testing the pepsin activity effect and a typical small intestinal luminal pH for testing the trypsin and chymotrypsin activity effects. The expression of both GH5-tCel5A1 and GH5-p4818 Cel5_2A endocellularases of the bacterial origins in the major commercial fungal protein production platforms such as _Trichoderma reseei_, _Humicola insolens_, _Aspergillus niger_ and yeast _Pichia pastoris_ and the subsequent expression effects on GH5-tCel5A1 and GH5-p4818 Cel5_2A endocellular glycosylation and protease resistance should be further investigated for future commercial implications. Small Molecular Size and Monomodular Structure of the Newly Characterized Processive Endocellulases  
These novel GH5-tCel5A1 and GH5-p4818 Cel5_2A processive cellulases were characterized to be a relatively small monomodular enzyme protein with a molecular weight of about 37 and 42 kDa [45,127]. [PERSON] [93] viewed that most single modular proteins would fold into one globular domain and polypeptides larger than 50 kDa typically form two or more domains. Thus, small molecular weight monomodular cellulases likely form various spheric shapes with a different radius size while bi-modular, larger molecular weight cellulases tend to show ellipsoid and tadpole shapes or other irregular shapes [97,98]. As shown by [PERSON] et al. (2019), the predicted GH5-p4818 Cel5_2A endocellular structure resembles a globular shape. [PERSON] et al. [45] reported that GH5-p4818 Cel5_2A was estimated to have a diameter of 4.6 nm calculated according to the model by [PERSON] [93]. Thus, GH5-tCel5A1, as reported by [PERSON] and [PERSON] [127], would have even a much smaller diameter compared with the GH5-p4818 Cel5_2A. [PERSON] et al. [18] reported that pore size diameters in various plant cell wall materials ranged between 3.5 and 5.2 nm. Several studies documented that physiologically pretreated lignocellulosic biomass materials and crystalline cellulose model substrates were associated with much larger pore diameters, ranging between 5.1-11.0 nm [94, 95, 96, 97]. Thus, these GH5-tCel5A1 and GH5-p4818 Cel5_2A processive cellulases should be effective in penetrating into microfibrillar internal surfaces of raw biomass materials such as fibre feeds and feedstocks because of its small molecular weight and size. Very few endocellulases have been reported in the current literature with the combined biochemical features of having a single module, a small molecular weight and size and being highly active in hydrolyzing crystalline celluloses and/or hemicelluloses. [PERSON] et al.