EC 2.1.1.365     
Accepted name: MMP 1-O-methyltransferase
Reaction: S-adenosyl-L-methionine + 3,3′-di-O-methyl-4α-mannobiose = S-adenosyl-L-homocysteine + 1,3,3′-tri-O-methyl-4α-mannobiose
Glossary: 3,3′-di-O-methyl-4α-mannobiose = 3-O-methyl-α-D-mannopyranosyl-(1→4)-3-O-methyl-α-D-mannopyranose
Other name(s): MeT1; 3-O-methylmannose polysaccharide 1-O-methyltransferase
Systematic name: S-adenosyl-L-methionine:3,3′-di-O-methyl-4α-mannobiose 1-O-methyltransferase
Comments: Requires Mg2+. The enzyme, characterized from the bacterium Mycolicibacterium hassiacum, participates in the biosynthesis of 3-O-methylmannose polysaccharides (MMP), which are intracellular polymethylated polysaccharides implicated in the modulation of fatty acid metabolism in nontuberculous mycobacteria. The methylation catalysed by this enzyme was shown to block the reducing end of 3,3′-di-O-methyl-α-mannobiose, a probable early precursor of the 3-O-methylmannose polysaccharides.
References:
1.  Ripoll-Rozada, J., Costa, M., Manso, J.A., Maranha, A., Miranda, V., Sequeira, A., Ventura, M.R., Macedo-Ribeiro, S., Pereira, P.JB. and Empadinhas, N. Biosynthesis of mycobacterial methylmannose polysaccharides requires a unique 1-O-methyltransferase specific for 3-O-methylated mannosides. Proc. Natl. Acad. Sci. USA 116 (2019) 835–844. [PMID: 30606802]
[EC 2.1.1.365 created 2020]