Ancestral versus Modern Substrate Scope in Family-1 Glycosidases

Experimental studies support that protein engineering based on ancestral sequence reconstruction often leads to variants with biotechnologically useful biomolecular properties. These may include high stability, enhanced conformational flexibility and a modified catalysis range. Carbohydrate-active enzymes have numerous applications related with the degradation and synthesis of carbohydrates and glycoconjugates. Here, we explore how ancestral reconstruction may impact substrate scope in glycosidases, highly diverse enzymes that catalyze the hydrolysis of glycosidic bonds in all living cells and find applications as catalysts of the reverse reaction. To this end, we screen a library of [~]500 potential glycosidase substrates for degradation by both, a modern family-1 glycosidase from Halothermothrix orenii and a putative ancestral family-1 glycosidase derived from sequence reconstruction at a bacterial-eukaryotic common ancestor. The modern enzyme is the better catalyst for most substrates. But the ancestral glycosidase is more efficient with flavonoid glycosides bearing large aglycon moieties. Analysis of the catalytic parameters for a selected set of substrates, alongside analysis of the library data using a supervised learning algorithm, support the hypothesis that the modern enzyme tends to become less catalytically efficient with increasing substrate size, while this trend is not observed for the ancestral glycosidase. Molecular simulations support that the ancestral catalysis pattern is linked to the existence of a highly flexible region of the ancestral structure and a cavity capable of accommodating large aglycons. Our results provide guidelines for the engineering of enzymes for the synthesis and hydrolysis of large glycoconjugates.