Defining pseudoenzymes in glycosylation pathways

Abstract

Glycosylation pathways regulate diverse cellular processes from protein quality control to host‐pathogen interactions and the enzymes that catalyze glycosidic linkages, glycosyltransferases (GTs), are a large super‐family of proteins that display extensive variation in primary sequence and three‐dimensional structure. A large fraction of GTs also display variations in key active site residues, but the functional and evolutionary implications of these variations are not well understood. In this talk, I will describe our ongoing efforts to map and classify GTs and pseudoGTs across the tree of life. A phylogenetic tree relating diverse GT‐A fold enzymes reveals that pseudoGTs evolved multiple independent times during evolution and variations in the catalytic base (xED‐Asp) correlate with the stereochemistry of glycosidic linkages in the acceptor substrate i.e., inverting vs retaining. Co‐evolutionary analysis reveals that active site variations in GTs are accommodated through compensatory interactions in distal functional sites associated with substrate recognition. Our studies support the “Red Queen” hypothesis in which the selective pressure to catalyze glycosidic linkages between diverse donor and acceptor substrates led to the emergence and expansion of pseudoGTs across the tree of life. Our findings have important implications for understanding other pseudoenzyme families such as pseudokinases.