title: Cellulase-lignin interactions-the role of carbohydrate-binding module and pH in non-productive binding.
abstract: Non-productive cellulase adsorption onto lignin is a major inhibitory mechanism preventing enzymatic hydrolysis of lignocellulosic feedstocks. Therefore, understanding of enzyme-lignin interactions is essential for the development of enzyme mixtures and processes for lignocellulose hydrolysis. We have studied cellulase-lignin interactions using model enzymes, Melanocarpus albomyces Cel45A endoglucanase (MaCel45A) and its fusions with native and mutated carbohydrate-binding modules (CBMs) from Trichoderma reesei Cel7A. Binding of MaCel45A to lignin was dependent on pH in the presence and absence of the CBM; at high pH, less enzyme bound to isolated lignins. Potentiometric titration of the lignin preparations showed that negatively charged groups were present in the lignin samples and that negative charge in the samples was increased with increasing pH. The results suggest that electrostatic interactions contributed to non-productive enzyme adsorption: Reduced enzyme binding at high pH was presumably due to repulsive electrostatic interactions between the enzymes and lignin. The CBM increased binding of MaCel45A to the isolated lignins only at high pH. Hydrophobic interactions are probably involved in CBM binding to lignin, because the same aromatic amino acids that are essential in CBM-cellulose interaction were also shown to contribute to lignin-binding.
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Finland. Electronic address: jenni.rahikainen@vtt.fi.
authors.forename: Jenni Liisa
authors.initials: JL
authors.lastname: Rahikainen
authors.forename: James David
authors.initials: JD
authors.lastname: Evans
authors.forename: Saara
authors.initials: S
authors.lastname: Mikander
authors.forename: Anna
authors.initials: A
authors.lastname: Kalliola
authors.forename: Terhi
authors.initials: T
authors.lastname: Puranen
authors.forename: Tarja
authors.initials: T
authors.lastname: Tamminen
authors.forename: Kaisa
authors.initials: K
authors.lastname: Marjamaa
authors.forename: Kristiina
authors.initials: K
authors.lastname: Kruus
mesh_terms: D000327:Adsorption; D020134:Catalytic Domain / Q000235:genetics; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008031:Lignin / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020037:Sordariales / Q000201:enzymology / Q000235:genetics; D055672:Static Electricity; D014242:Trichoderma / Q000201:enzymology / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; C036909:lignocellulose; D002482:Cellulose; D008031:Lignin; D002480:Cellulase
keywords: CBM; Cellulase; Electrostatic interaction; EnzHR; Lignin; Lignocellulose; MCC; MaCel45A; Melanocarpus albomyces Cel45A; Non-productive binding; TrCel7A; Trichoderma reesei Cel7A; enzymatic hydrolysis residue; microcrystalline cellulose