**7. Concluding remarks**

Microorganisms use an arsenal of GHs to degrade plant cell walls, in order to establish themselves in their host. Similar mechanisms are thought to be used in their own plant cell wall modification, since plant cell walls embrace several types of carbohydrates with a variety of structures and biological functions. For sugarcane biomass deconstruction, the first step proposed is the use of pectinases to release pectins, such as endopolygalacturonases, AFases, and β-galactosidases, along with pectin methylesterases. Lichenases are used to hydrolyze mixed linked β-D-glucan. The remaining polymers, cellulose, and hemicelluloses, would have to be treated with a mixture of enzymes like endo-β-xylanases, α-arabinofuranosidases, xyloglucanases, α-xylosidases, and β-galactosidases. Finally, cellulose could be the substrate of endo-β-glucanases, cellobiohydrolases, and β-glucosidases [88].

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Besides many studies focusing on microorganism enzymes to optimize E2G production, this work has evaluated the plant enzymes that are assumed to display similar activities. Since plant GHs perform cell wall breakage and expansion, a deeper investigation of their structure could be performed in order to produce more efficient chimeric enzymes to be used in enzymatic cocktails. It is difficult to establish GH functions from their amino acid sequences because proteins from the same GH family may have diverse substrates and roles [8]. However, we were able to predict functions for the GHs identified in the cell wall proteomes of sugarcane and *B. distachyon*. Thus, the mentioned GH1, some GH3 and GH17 were predicted to have a β-glucosidase activity. Other GH3 had possible β-xylosidase and AFase activities, the latter also predicted for GH51. The GH27 and GH35 families were predicted to have α- and β-galactosidase activity, respectively. Nevertheless, it is crucial to mention that in order to precisely characterize the function of a given protein, one should perform biochemical analyses, involving purification, characterization of substrates, as well as genetic studies on mutants in well-characterized model plants.

Therefore, this work has contributed to provide target proteins that could possibly be used in future research to facilitate cheaper E2G production, besides allowing a more detailed analysis of the cell wall proteomes of the grasses, sugarcane and *B. distachyon*.
