© 2006 The Japanese Biochemical Society.
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A Retaining Endo-ß-Mannosidase from a Dicot Plant, Cabbage
Department of Chemistry, Graduate School of Science, Osaka University, Osaka 560-0043
* To whom correspondence should be addressed: Tel.: +81-6-6850-5380, Fax: +81-6-6850-5383, E-mail: suhase{at}chem.sci.osaka-u.ac.jp
An endo-ß-mannosidase [EC 3.2.1.152
[EC]
, glycoside hydrolase family 2], which hydrolyzes the Manß1-4GlcNAc linkage of N-glycans in an endo-manner, has been found in plant tissues [Ishimizu, T., Sasaki, A., Okutani, S., Maeda, M., Yamagishi, M., and Hase, S. (2004) J. Biol. Chem. 279, 38555–38562]. So far, this glycosidase has been purified only from a monocot plant, a lily. Here, an endo-ß-mannosidase was purified from a dicot plant, cabbage (Brassica oleracea), and characterized. The cabbage endo-ß-mannosidase consists of four polypeptides. These four polypeptides are encoded by a single gene, whose nucleotide sequence is homologous to those of the lily and Arabidopsis endo-ß-mannosidase genes. 1H NMR analysis of the stereochemistry of the hydrolysis of pyridylaminated (PA) Man
1-6Manß1-4GlcNAcß1-4GlcNAc showed that the cabbage endo-ß-mannosidase is a retaining glycoside hydrolase, as are other glycoside hydrolase family 2 enzymes. The enzymatic characteristics, including substrate specificity, of the cabbage enzyme are very similar to those of the lily enzyme. These endo-ß-mannosidases specifically act on MannMan1-6Manß1-4GlcNAcß1-4GlcNAc-PA (n = 0 to 2). These results suggest that the endo-ß-mannosidase is present in at least the angiosperms, and has common roles, such as the degradation of N-glycans.
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