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Publication Abstract from PubMed

N-linked glycans play key roles in protein folding, stability, and function. Biosynthetic modification of N-linked glycans, within the endoplasmic reticulum, features sequential trimming and readornment steps. One unusual enzyme, endo-alpha-mannosidase, cleaves mannoside linkages internally within an N-linked glycan chain, short circuiting the classical N-glycan biosynthetic pathway. Here, using two bacterial orthologs, we present the first structural and mechanistic dissection of endo-alpha-mannosidase. Structures solved at resolutions 1.7-2.1 A reveal a (beta/alpha)(8) barrel fold in which the catalytic center is present in a long substrate-binding groove, consistent with cleavage within the N-glycan chain. Enzymatic cleavage of authentic Glc(1/3)Man(9)GlcNAc(2) yields Glc(1/3)-Man. Using the bespoke substrate alpha-Glc-1,3-alpha-Man fluoride, the enzyme was shown to act with retention of anomeric configuration. Complexes with the established endo-alpha-mannosidase inhibitor alpha-Glc-1,3-deoxymannonojirimycin and a newly developed inhibitor, alpha-Glc-1,3-isofagomine, and with the reducing-end product alpha-1,2-mannobiose structurally define the -2 to +2 subsites of the enzyme. These structural and mechanistic data provide a foundation upon which to develop new enzyme inhibitors targeting the hijacking of N-glycan synthesis in viral disease and cancer.

Structural and mechanistic insight into N-glycan processing by endo-alpha-mannosidase.,Thompson AJ, Williams RJ, Hakki Z, Alonzi DS, Wennekes T, Gloster TM, Songsrirote K, Thomas-Oates JE, Wrodnigg TM, Spreitz J, Stutz AE, Butters TD, Williams SJ, Davies GJ Proc Natl Acad Sci U S A. 2012 Jan 4. PMID:22219371^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.