Lignocellulose-degrading chimeras: Emerging perspectives for catalytic aspects, stability, and industrial applications

A major obstacle to the bioconversion of lignocellulosic biomass is its complex structure and recalcitrance. Chimeric enzymes, by expressing different enzymatic reactions in a single setup with desirable and improved properties such as stability at high temperatures, wide pH range, high catalytic efficiency, and turnover number, prove to be an environment-friendly solution for the degradation of lignocellulosics compared to traditional methods. This review provides comprehensive information on the design and construction strategies (tandem fusion, fusion through linker, and domain insertion) and the biochemical properties such as catalytic efficiency, substrate affinity, stability, activity, expression, and secretion of lignocellulose-degrading chimeras. The fusion of non-catalytic proteins, including carbohydrate-binding modules, plant expansins, expansin-like proteins, anchor proteins, cohesin-dockerin, SpyTag-SpyCatcher, and osmotically induced families of proteins which by increasing the proximity between enzyme and substrate, facilitating the recognition of specific cleavage sites in the substrate or by removing hydrogen bonds between cellulose microfibrils and cellulose-hemicellulose complexes, serve as an effective strategy to improve the hydrolysis of lignocellulosic substrates has been discussed. To highlight industrial relevance, a comparative account on the bioprocessing of lignocellulosic substrates by lignocellulose-degrading chimeras is presented. As the knowledge base continues to expand on complementary molecular, structural, and synthetic biology methods, more mechanistic insights will be gained for further perfecting the catalytic toolbox of lignocellulose-degrading chimeras vis-à-vis the versatility of applications.