Endo-β-Mannosidase, a Plant Enzyme Acting on N-Glycans

Abstract

Endo-β-mannosidase (EC 3.1.2.152), which hydrolyzes Manβ1-4GlcNAc linkages in the core structure of N-glycans, has been found in higher plants. Recently, purification of this enzyme and molecular cloning of its gene have been accomplished. Orthologues of endo-β-mannosidase gene have been found only in plant species, suggesting that this enzyme has plant-specific functions. This endoglycosidase has unique substrate specificity, hydrolyzing the Manβ1-4GlcNAc linkage in (Man)_nManα1-6Manβ1-4GlcNAcβ1-4GlcNAc (n=0-2). These substrates are generated from high-mannose type N-glycans by the action of a jack bean α-mannosidase-like enzyme, which prefers to hydrolyze Manα1-3Manβ linkages. It is therefore likely that endo-β-mannosidase and jack bean α-mannosidase-like enzyme cooperatively hydrolyze highmannose type N-glycans to N, N'-diacetylchitobiose in plant cells. In addition, endo-β-mannosidase has transglycosylation activity that can form a β-mannoside linkage, for which anomeric regulation during chemical synthesis reaction is difficult.