Asn-linked oligosaccharides are extensively modified during transit through the secretory pathway, first by trimming of the nascent glycan chains and subsequently by initiating and extending multiple oligosaccharide branches from the tri-mannosyl glycan core. Glycan extension is highly ordered and hierarchal based on the precise substrate specificities of the individual biosynthetic enzymes. Few of these enzymes have been well characterized for details of substrate interactions due to challenges associated with their recombinant expression. We developed a modular expression strategy for production of human glycoenzymes as secreted catalytic domain fusion proteins and have recently advanced several of these enzymes to structural studies in complex with substrate analogs. The goals of these studies are to examine the structural basis for substrate recognition and regiospecific glycan modification. Structural studies on several key <i>N</i>-glycan biosynthetic enzymes will be presented. In each case extensive substrate interactions have been observed that explain their precise specificities for glycan modification. These data demonstrate that mammalian glycosylation enzymes employ complementary active site modules for glycan donor and acceptor recognition and modification that provide templates for glycan biosynthesis in mammalian cells.

Glycosyltransferase structures as modular templates for diverse glycan synthesis

ACS Spring Meeting 2021

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