The Enzyme Database

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Accepted name: dolichyl-P-Man:Man5GlcNAc2-PP-dolichol α-1,3-mannosyltransferase
Reaction: dolichyl β-D-mannosyl phosphate + α-D-Man-(1→2)-α-D-Man-(1→2)-α-D-Man-(1→3)-[α-D-Man-(1→6)]-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-α-D-GlcNAc-diphosphodolichol = α-D-Man-(1→2)-α-D-Man-(1→2)-α-D-Man-(1→3)-[α-D-Man-(1→3)-α-D-Man-(1→6)]-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-α-D-GlcNAc-diphosphodolichol + dolichyl phosphate
For diagram of dolichyltetradecasaccharide biosynthesis, click here
Other name(s): Man5GlcNAc2-PP-Dol mannosyltransferase; ALG3; dolichyl-P-Man:Man(5)GlcNAc(2)-PP-dolichyl mannosyltransferase; Not56-like protein; Alg3 α-1,3-mannosyl transferase; Dol-P-Man:Man5GlcNAc2-PP-Dol α-1,3-mannosyltransferase; dolichyl β-D-mannosyl phosphate:D-Man-α-(1→2)-D-Man-α-(1→2)-D-Man-α-(1→3)-[D-Man-α-(1→6)]-D-Man-β-(1→4)-D-GlcNAc-β-(1→4)-D-GlcNAc-diphosphodolichol α-1,3-mannosyltransferase
Systematic name: dolichyl β-D-mannosyl phosphate:α-D-Man-(1→2)-α-D-Man-(1→2)-α-D-Man-(1→3)-[α-D-Man-(1→6)]-β-D-Man-(1→4)-β-D-GlcNAc-(1→4)-α-D-GlcNAc-diphosphodolichol 3-α-D-mannosyltransferase (configuration-inverting)
Comments: The formation of N-glycosidic linkages of glycoproteins involves the ordered assembly of the common Glc3Man9GlcNAc2 core-oligosaccharide on the lipid carrier dolichyl diphosphate. Early mannosylation steps occur on the cytoplasmic side of the endoplasmic reticulum with GDP-Man as donor, the final reactions from Man5GlcNAc2-PP-dolichol to Man9Glc-NAc2-PP-dolichol on the lumenal side use dolichyl β-D-mannosyl phosphate. The first step of this assembly pathway on the luminal side of the endoplasmic reticulum is catalysed by ALG3.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Sharma, C.B., Knauer, R. and Lehle, L. Biosynthesis of lipid-linked oligosaccharides in yeast: the ALG3 gene encodes the Dol-P-Man:Man5GlcNAc2-PP-Dol mannosyltransferase. Biol. Chem. 382 (2001) 321–328. [PMID: 11308030]
2.  Cipollo, J.F. and Trimble, R.B. The accumulation of Man(6)GlcNAc(2)-PP-dolichol in the Saccharomyces cerevisiae Δalg9 mutant reveals a regulatory role for the Alg3p α1,3-Man middle-arm addition in downstream oligosaccharide-lipid and glycoprotein glycan processing. J. Biol. Chem. 275 (2000) 4267–4277. [PMID: 10660594]
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