Engineering and Comparative Characteristics of Double Carbohydrate Binding Modules as a Strength Additive for Papermaking Applications

Abstract

In this study, four engineered proteins containing two family 1 and/or family 3 carbohydrate binding modules (CBMs) were constructed and expressed as soluble forms in Escherichia coli. Their binding performances and effect on paper's mechanical properties were comprehensively studied with the aim to design suitably engineered CBMs as novel biomaterials for use in the production of new cellulose materials. The recombinant engineered double CBMs exhibited obvious differences in their adsorption to different cellulosic substrates. The CBM3-GS-CBM3 was the most effective in enhancing paper mechanical properties in terms of folding endurance (27.4%) and tensile strength (15.5%) among the four engineered double CBMs, but it gave rise to only a slight increase in bursting strength (3.1%). On the other hand, CBM1-NL-CBM1 achieved a significant simultaneous increase in tensile strength (12.6%) and burst strength (8.8%), as well as folding endurance (16.7%). Unexpectedly, CBM3-GS-CBM1 and CBM3-NL-CBM1 had the lowest effective paper property improvement. The differences in types of CBMs and linker peptides in engineered double CBMs may contribute to the considerable differences in their cellulose binding and paper property modification. Our data suggested that CBM1-NL-CBM1 may provide a better upgrade of the secondary pulp, which makes it very suitable for fiber recycling. Meanwhile, CBM3-GS-CBM3 may have particular potential for paper manufacture requiring high folding endurance.