Energy security, climate change, and economic development are the driving forces behind the increasing focus on biofuel production worldwide. Lignocellulose can provide ample raw materials for biofuel production, via its hydrolysis and the fermentation of the released sugars. Currently, lignocellulases are often used to catalyze this step, which hydrolyze the β-1, 4 glycosidic linkages in lignocellulose. These enzymes offer a good starting point for enhancing the overall economics of biofuel production. To reduce cost in biofuel production, there is a need for enzymes with improved activity and broader substrate range. The rapid development of a variety of protein engineering techniques has facilitated the development of novel biocatalysts with improved properties. A range of specific properties can be enhanced in enzymes, including the catalytic activity, thermostability, and specificity, under industrial conditions.
IEA. World Energy Outlook (2010). Available at: http://worldenergyoutlook.org/media/weo2010.pdf (Last accessed January2018).
3.
EisentrautA. Sustainable production of second-generation biofuels (2010). Available at: https://iea.org/publications/freepublications/publication/second_generation_biofuels.pdf (Last accessed January2018).
4.
SissineF. Renewable Fuel Standard Program (RFS2) Regulatory Impact Analysis, Technical Report EPA-420-R-10-006. Assessment and Standards Division, Office of Transportation and Air Quality, 2010.
5.
EPA. EPA Lifecycle Analysis of Greenhouse Gas Emissions from Renewable Fuels (2010). Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi/P1006DVI.PDF?Dockey=P1006DVI.PDF (Last accessed January2018).
6.
PradeRA. Xylanases: From biology to biotechnology. Biotechnol Genet Eng Rev, 1996; 13:101–132.
KulkarniN, ShendyeA, RaoM. Molecular and biotechnological aspects of xylanases. FEMS Microbiol Rev, 1999; 23:411–56.
9.
BegQK, KapoorM, MahajanL, HoondalGS. Microbial xylanases and their industrial applications: A review. Appl Microbiol Biotechnol, 2001; 56:326–338. doi:10.1007/s002530100704.
10.
GadgilNJ, DaginawalaHF, ChakrabartiT, KhannaP. Enhanced cellulase production by a mutant of Trichoderma reesei. Enzyme Microb Technol, 1995; 17:942–946.
11.
VuVH, PhamTA, KimK. Fungal strain improvement for cellulase production using repeated and sequential mutagenesis. Mycobiology, 2009; 37:267–271.
12.
McCarterSL, AdneyWS, VinzantTB, et al.Exploration of cellulose surface-binding properties of acidothermus cellulolyticus Cel5A by site-specific mutagenesis. Appl Biochem Biotechnol, 2002; 98–100:273–287. doi:10.1385/ABAB:98-100:1-9:273.
13.
SongL, SiguierB, DumonC, BozonnetS, O'DonohueMJ. Engineering better biomass-degrading ability into a GH11 xylanase using a directed evolution strategy. Biotechnol Biofuels, 2012; 5:3. doi:10.1186/1754-6834-5-3.
14.
RignallTR, BakerJO, McCarterSL, et al.Effect of single active-site cleft mutation on product specificity in a thermostable bacterial cellulase. Biotechnol Fuels Chem, 2002; 98–100:383–94.
15.
NamKH, KimS-J, HwangKY. Crystal structure of CelM2, a bifunctional glucanase-xylanase protein from a metagenome library. Biochem Biophys Res Commun, 2009; 383:183–186. doi:10.1016/j.bbrc.2009.03.149.
ArnoldFH, WintrodePL, MiyazakiK, GershensonA. How enzymes adapt: Lessons from directed evolution. Trends Biochem Sci, 2001; 26:100–106.
18.
ArnoldFH. Combinatorial and computational challenges for biocatalyst design. Nature, 2001; 409:253–257.
19.
BenkovicSJ, Hammes-SchifferS. A perspective on enzyme catalysis. Science, 2003; 301(5637):1196–1202.
20.
DwyerMA, LoogerLL, HellingaHW. Computational design of a biologically active enzyme. Science, 2004; 304:1967–1971. (Retraction published 2008;319(5863):569)
21.
BakerJO, McCarleyJR, LovettR, et al.Catalytically enhanced endocellulase CeI5A from Acidothermus cellulolyticus. Appl Biochem Biotechnol, 2005; 121–124:129–48.
22.
SakonJ, AdneyWS, HimmelME, ThomasSR, KarplusPA. Crystal structure of thermostable family 5 Endocellulase E1 from Acidothermus cellulolyticus in complex with cellotetraose. Biochemistry, 1996; 35:10648–10660.
23.
Percival ZhangY-H, HimmelME, MielenzJR. Outlook for cellulase improvement: screening and selection strategies. Biotechnol Adv, 2006; 24:452–481. doi:10.1016/j.biotechadv.2006.03.003.
24.
MurashimaK, KosugiA. Thermostabilization of cellulosomal endoglucanase EngB from Clostridium cellulovorans by in vitro DNA recombination with non‐cellulosomal endoglucanase EngD. Mol Microbiol, 2002; 45:617–626.
25.
González-BlascoG, Sanz-AparicioJ, GonzálezB, HermosoJA, PolainaJ. Directed evolution of β-glucosidase A from Paenibacillus polymyxa to thermal resistance. J Biol Chem, 2000; 275:13708–13712.
26.
SriprapundhD, VieilleC, ZeikusJG. Directed evolution of Thermotoga neapolitana xylose isomerase: High activity on glucose at low temperature and low pH. Protein Eng, 2003; 16:683–690.
27.
WenT-N, ChenJ-L, LeeS-H, YangN-S, ShyurL-F. A truncated fibrobacter succinogenes 1, 3− 1, 4-β-d-glucanase with improved enzymatic activity and thermotolerance. Biochemistry, 2005; 44:9197–9205.
28.
FenelF, ZittingA-J, KantelinenA. Increased alkali stability in Trichoderma reesei endo-1, 4-β-xylanase II by site directed mutagenesis. J Biotechnol, 2006; 121:102–107.
29.
BeliënT, JoyeIJ, DelcourJA, CourtinCM. Computational design-based molecular engineering of the glycosyl hydrolase family 11 B. subtilis XynA endoxylanase improves its acid stability. Protein Eng Des Sel, 2009; 22(10):587–596.
30.
SpadiutO, NguyenT-T, HaltrichD. Thermostable variants of pyranose 2-oxidase showing altered substrate selectivity for glucose and galactose. J Agric Food Chem, 2010; 58:3465–3471.
31.
ZhangZ-G, YiZ-L, PeiX-Q, WuZ-L. Improving the thermostability of Geobacillus stearothermophilus xylanase XT6 by directed evolution and site-directed mutagenesis. Bioresour Technol, 2010; 101:9272–9278.
32.
HokansonCA, CappuccilliG, OdinecaT, et al.Engineering highly thermostable xylanase variants using an enhanced combinatorial library method. Protein Eng Des Sel, 2011; 24:597–605. doi:10.1093/protein/gzr028.
33.
HuangJ-W, ChengY-S, KoT-P, et al.Rational design to improve thermostability and specific activity of the truncated Fibrobacter succinogenes 1, 3-1, 4-β-D-glucanase. Appl Microbiol Biotechnol, 2012; 94:111–121.
34.
SrikrishnanS, RandallA, BaldiP, Da SilvaNA. Rationally selected single‐site mutants of the Thermoascus aurantiacus endoglucanase increase hydrolytic activity on cellulosic substrates. Biotechnol Bioeng, 2012; 109:1595–1599.
35.
YeX, ZhangC, ZhangY-HP. Engineering a large protein by combined rational and random approaches: Stabilizing the Clostridium thermocellum cellobiose phosphorylase. Mol Biosyst, 2012; 8:1815–1823.
36.
AnbarM, GulO, LamedR, SezermanUO, BayerEA. Improved thermostability of Clostridium thermocellum endoglucanase Cel8A by using consensus-guided mutagenesis. Appl Environ Microbiol, 2012; 78:3458–3464.
37.
WangY, YuanH, WangJ, YuZ. Truncation of the cellulose binding domain improved thermal stability of endo-β-1, 4-glucanase from Bacillus subtilis JA18. Bioresour Technol, 2009; 100:345–349.
38.
YiZ-L, PeiX-Q, WuZ-L. Introduction of glycine and proline residues onto protein surface increases the thermostability of endoglucanase CelA from Clostridium thermocellum. Bioresour Technol, 2011; 102:3636–3638.
39.
PeiX-Q, YiZ-L, TangC-G, WuZ-L. Three amino acid changes contribute markedly to the thermostability of β-glucosidase BglC from Thermobifida fusca. Bioresour Technol, 2011; 102:3337–3342.
40.
LeeH-L, ChangC-K, JengW-Y, WangA-HJ, LiangPH. Mutations in the substrate entrance region of β-glucosidase from Trichoderma reesei improve enzyme activity and thermostability. Protein Eng Des Sel, 2012; 25(11):733–740
