Modification of cellulase with smart-green polymers to promote low-cost and cleaner production of cellulosic ethanol

Abstract

Cellulosic ethanol produced using the enzymatic method is promising; however, developing an efficient and green cellulase hydrolysis system to cut the cost of cellulosic ethanol and promote cleaner biofuel production remains challenging. Herein, based on the fact that multiple hydrogen bond can be generated between poly (methyl acrylic acid-co-acrylic acid) and gelatin, cellulase was first covalently bonded to the copolymer and then mixed with gelatin, to endow the cellulase with ideal upper critical solution temperature (UCST). As a result, the affinity between cellulase and the substrate did not decrease significantly after the modification (the Km value of modified cellulase (4.62 g/L) was not significantly different from that of free cellulase (4.55 g/L)). The enzymes can be switched on-demand between free state (above 36 °C), enabling high hydrolysis reactivity for insoluble substrates such as paper or corn stalks, and fixed state (at 4 °C), facilitating enzymes separation and reuse (the modified cellulase still has 58.2% of its initial activity for 20 batches). Thus, the cost of cellulosic ethanol production could be significantly reduced in the precondition of high catalytic efficiency. Furthermore, the system presents nontoxic and biodegradable properties. The system can be completely degraded in soil after 7 days and the inhibition rate of the degraded products on luminescent bacteria was only 2%, which can promote cleaner cellulosic biofuel production.