Structure of human endo-α-1,2-mannosidase (MANEA), an antiviral host-glycosylation target

Mammalian protein N-linked glycosylation is critical for glycoprotein folding, quality control, trafficking, recognition and function. N-linked glycans are synthesized from Glc3Man9GlcNAc2 precursors that are trimmed and modified in the endoplasmic reticulum (ER) and Golgi apparatus by glycoside hydrolases and glycosyltransferases. Endo-α-1,2-mannosidase (MANEA) is the sole endo-acting glycoside hydrolase involved in N-glycan trimming and unusually is located within the Golgi, where it allows ER escaped glycoproteins to bypass the classical N-glycosylation trimming pathway involving ER glucosidases I and II. There is considerable interest in the use of small molecules that disrupt N-linked glycosylation as therapeutic agents for diseases such as cancer and viral infection. Here we report the structure of the catalytic domain of human MANEA and complexes with substrate-derived inhibitors, which provide insight into dynamic loop movements that occur upon substrate binding. We reveal structural features of the human enzyme that explain its substrate preference and the mechanistic basis for catalysis. The structures inspired the development of new inhibitors that disrupted host protein N-glycan processing of viral glycans and reduced infectivity of bovine viral diarrhea and dengue viruses in cellular models. These results may contribute to efforts of developing broad-spectrum antiviral agents and bring about a more detailed view of the biology of mammalian glycosylation.