Activity and stability of hyperthermostable cellulases and xylanases in ionic liquids

Abstract

The biochemical conversion route in the utilization of biomass has required intensive development of processing methods for reducing recalcitrance of cellulose to enzymatic hydrolysis. Since discovering hydrophilic ionic liquids (ILs) are efficient lignocellulose solvents, considerable efforts have been made to demonstrate their potential applications in cellulose hydrolysis. However, most of the commercial lignocellulose hydrolyzing enzymes are largely deactivated or inhibited in the presence of even low concentrations of ILs. The link found between enzyme thermostability and IL tolerance leads to the consideration that hyperthermostable enzymes are good candidates to be used together with ILs. Hyperthermostable cellulases and xylanases that are highly tolerant to aqueous solutions of ILs show resistance to competitive inhibition by IL cations and have lower amounts of structural motifs (loop and helix structures) that are prone to denaturation by IL anions. In addition, they have a net negative protein surface charge that contributes to repulsion of anions. This review provides recent developments in understanding the behaviour of hyperthermostable cellulases and xylanases in ILs by elucidating protein-IL interactions. It also outlines the current research demonstrating the potential of rational enzyme engineering to improve enzyme tolerance to ILs based on comprehension of IL-induced deactivation mechanisms.

Enhanced activity of hyperthermostable Pyrococcus horikoshii endoglucanase in superbase ionic liquids

“…PhEG was slightly activated in the presence of 40% [TMGH]n-PrCOO (Rahikainen et al 2018 ), and enzyme activation by ILs has also been observed in other hyperthermophilic endoglucanases (Hebal et al 2021 ). This phenomenon has been proposed to reflect the need for salt to achieve maximal enzyme activity (Ajloo et al 2013 ; Gladden et al 2014 ).…”

“…Dissolved cellulose can be precipitated away from the IL solution using an antisolvent. However, traces of ILs (in the range of 10–15%) may remain in the substrate after precipitation (Engel et al 2010 ), and most commercial cellulases are inhibited or deactivated by even low amounts of ILs (Wahlström and Suurnäkki 2015 ; Nemestóthy et al 2017 ; Hebal et al 2021 ). Therefore, the discovery or development of new enzymes with greater tolerance towards ILs is a prerequisite for the development of lignocellulose processes that use ILs.…”

“…Typically, the highly IL-tolerant endoglucanases and β -glucosidases originate from hyperthermophilic microbes (Hebal et al 2021 ), which suggests a link between enzyme thermostability and IL tolerance (Ferdjani et al 2011 ; Ilmberger et al 2012 ). A hyperthermophilic GH5 endoglucanase (PhEG) with the capability of hydrolysing crystalline cellulose from the hyperthermophilic archaon Pyrococcus horikoshii has been reported previously (Ando et al 2002 ).…”

Cryostorage of unstable N-acetylglucosaminyltransferase-V by synthetic zwitterions

“…Notably, the activity in the 5 and 10 wt% VimC 3 S solutions was significantly higher than that in water. An increase in enzymatic activity in another IL-containing solution has been reported, 25 and this may be the case. Although the mechanism of this increase is unclear, and further analyses are needed to elucidate the precise mechanisms, we speculate that the ion interactions between ZIs and the surface charges of GnT-V possibly affect the structure of GnT-V.…”

Thermostable Cellulases / Xylanases From Thermophilic and Hyperthermophilic Microorganisms: Current Perspective

“…Metagenomics are widely used as very powerful techniques to identify, Isolate, and characterized novel thermostable enzymes with efficient catalytic activities from extreme environment which includes various environment that are usually characterized by extreme temperature like hot springs, deserts, compost, hydrocarbon reservoirs, hydrothermal vents, e. t.c. ( Zarafeta et al, 2016 ; Madhavan et al, 2017b ; Hebal et al, 2021 ). The ability of a microbes to survive in these extreme habitat makes their protein to be highly thermostable.…”