Regulation of Substrate Specificity of Plant α-Mannosidase by Cobalt Ion:In VitroHydrolysis of High-Mannose TypeN-Glycans by Co²⁺-ActivatedGinkgoα-Mannosidase

Man2C1, an α-mannosidase, is involved in the trimming of free oligosaccharides in the cytosol

“…Manα1-6(Manα1-3)Manα1-6(Manα1-3)Manβ1-4GlcNAc [48]. Indeed the Co 2+ -activated enzyme has been isolated in Gingko seeds, and the substrate specificity of this enzyme is quite different from that of cytoplasmic α-mannosidase from animal cells [49,50]. Moreover, in budding yeast, the free oligosaccharide degradation after the release by PNGase was mainly carried out by a cytosol/vacuole α-mannosidase, termed Ams1p [51].…”

α-Mannosidase Involved in Turnover of Plant Complex TypeN-Glycans in Tomato (Lycopersicum esculentum) Fruits

“…After centrifugation, an aliquot (30 ml) of the reaction mixture was analyzed by SF-HPLC, as described in previous papers. 15,16) Purification of tomato -mannosidase. Unless otherwise stated, all purification steps were carried out at 4 C. During purification, pNP--Man was used as the substrate in measuring -mannosidase activity.…”

“…Since increases inmannosidase activities during seed germination of rice or Vicia sativa have been reported 3,14) this type of glycosidase, involved in degradation of N-glycans, appears to play a critical role in the development of plant cells. As part of a study to elucidate biological significance of degradation of N-glycans by -mannosidase in plants, in our previous studies 15,16) we isolated an -mannosidase from Gingko biloba seeds that was activated by Co 2þ and preferred high mannose type N-glycans with one GlcNAc residue (a GN1-type structure) generated by endo--N-acetylglucosaminidase (ENGase) to those with the chitobiosyl unit (a GN2-type structure) generated by a peptide:N-glycanase (PNGase), suggesting that this -mannosidase is involved in the degradation of high-mannose type free N-glycans. Furthermore, recently we found significant glycoform changes in free high-mannose type N-glycans during tomato fruit ripening, indicating that changes in -mannosidase activity occur during fruit maturation.…”

Changes in Structural Features of FreeN-Glycan and Endoglycosidase Activity during Tomato Fruit Ripening

“…Concerning the cytosolic -mannosidase involved in the degradation of high-mannose type free N-glycans, the plant enzyme has not been completely identified and fully characterized, although the animal enzyme has been well characterized. [22][23][24] In previous studies, 25,26) however, we purified an -mannosidase from Ginkgo seeds that was activated by cobalt ion and preferred highmannose type glycans with one GlcNAc residue rather than those with the chitobiosyl unit. Since these enzymatic properties are very similar to those of animal cytosolic -mannosidase [22][23][24] that has been thought to be involved in the degradation of high-mannose type free N-glycans produced by PNGase and ENGase in animal cells, [19][20][21][22] Ginkgo -mannosidase might be responsible for the degradation of high-mannose type free N-glycans in the cytosol.…”