Casein-based scaffold for artificial cellulosome design

Cellulosomal systems are known as highly efficient biocatalysts in the degradation of lignocellulosic biomass in nature, but they remain unsuitable for industrial applications. In seeking alternatives to natural cellulosomes, casein was chosen as a scaffold for cellulase clustering. Casein is recognized as an excellent substrate for microbial transglutaminase (MTG) because it contains naturally reactive glutamine and lysine residues. A substrate peptide containing an MTG-reactive lysine residue was inserted into the C-terminus of the endoglucanase Cel5A and Cel6A from Thermobifida fusca using genetic engineering. The engineered cellulases, EG(Cel5A) and EG(Cel6A), were conjugated onto casein in different ratios by an MTG-mediated site-specific protein crosslinking reaction. Overall, a more than two-fold increase was observed when EG(Cel5A) was conjugated onto N,N-dimethylcasein, but a small or no change was observed for EG(Cel6A).