title: Interactions between Cellulolytic Enzymes with Native, Autohydrolysis, and Technical Lignins and the Effect of a Polysorbate Amphiphile in Reducing Nonproductive Binding.
abstract: Understanding enzyme-substrate interactions is critical in designing strategies for bioconversion of lignocellulosic biomass. In this study we monitored molecular events, in situ and in real time, including the adsorption and desorption of cellulolytic enzymes on lignins and cellulose, by using quartz crystal microgravimetry and surface plasmon resonance. The effect of a nonionic surface active molecule was also elucidated. Three lignin substrates relevant to the sugar platform in biorefinery efforts were considered, namely, hardwood autohydrolysis cellulolytic (HWAH), hardwood native cellulolytic (MPCEL), and nonwood native cellulolytic (WSCEL) lignin. In addition, Kraft lignins derived from softwoods (SWK) and hardwoods (HWK) were used as references. The results indicated a high affinity between the lignins with both, monocomponent and multicomponent enzymes. More importantly, the addition of nonionic surfactants at concentrations above their critical micelle concentration reduced remarkably (by over 90%) the nonproductive interactions between the cellulolytic enzymes and the lignins. This effect was hypothesized to be a consequence of the balance of hydrophobic and hydrogen bonding interactions. Moreover, the reduction of surface roughness and increased wettability of lignin surfaces upon surfactant treatment contributed to a lower affinity with the enzymes. Conformational changes of cellulases were observed upon their adsorption on lignin carrying preadsorbed surfactant. Weak electrostatic interactions were determined in aqueous media at pH between 4.8 and 5.5 for the native cellulolytic lignins (MPCEL and WSCEL), whereby a ∼20% reduction in the enzyme affinity was observed. This was mainly explained by electrostatic interactions (osmotic pressure effects) between charged lignins and cellulases. Noteworthy, adsorption of nonionic surfactants onto cellulose, in the form cellulose nanofibrils, did not affect its hydrolytic conversion. Overall, our results highlight the benefit of nonionic surfactant pretreatment to reduce nonproductive enzyme binding while maintaining the reactivity of the cellulosic substrate.
authors.affiliation: Department of Forest Biomaterials, North Carolina State University , Raleigh, North Carolina 27695-8005, United States.
authors.forename: Consuelo
authors.initials: C
authors.lastname: Fritz
authors.affiliation: Department of Forest Biomaterials, North Carolina State University , Raleigh, North Carolina 27695-8005, United States.
authors.forename: Ana
authors.initials: A
authors.lastname: Ferrer
authors.affiliation: Department of Forest Biomaterials, North Carolina State University , Raleigh, North Carolina 27695-8005, United States.
authors.forename: Carlos
authors.initials: C
authors.lastname: Salas
authors.affiliation: Department of Forest Biomaterials, North Carolina State University , Raleigh, North Carolina 27695-8005, United States.
authors.forename: Hasan
authors.initials: H
authors.lastname: Jameel
authors.affiliation: Department of Forest Biomaterials, North Carolina State University , Raleigh, North Carolina 27695-8005, United States.|Bio-Based Colloids and Materials, Department of Forest Products Technology and Centre of Excellence on "Molecular Engineering of Biosynthetic Hybrid Materials" (HYBER), Aalto University , FIN-00076 Aalto, Espoo, Finland.
authors.forename: Orlando J
authors.initials: OJ
authors.lastname: Rojas
mesh_terms: D000327:Adsorption; D018533:Biomass; D044602:Cellulases / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008031:Lignin / Q000737:chemistry*; D011136:Polysorbates / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D058525:Quartz Crystal Microbalance Techniques; D055672:Static Electricity; D020349:Surface Plasmon Resonance
chemical_list: D011136:Polysorbates; C036909:lignocellulose; C076151:Kraft lignin; D008031:Lignin; D044602:Cellulases